Chapter VII: Section I: The Bones and Joints (2)

*b.* The small anterior bones of the ventral portion of the shoulder-girdle (Figs. 24 _cl._, 31), I, like Cuvier and others, regard as *clavicles*. Dugès (n. 33) names them ‘_acromial_.’ Each bone is narrower than the coracoid, smaller internally (_m_), broader externally (_l_), and articulates by this broader end with the cartilage uniting the dorsal and ventral portions; the inner extremity rests upon the epicoracoid. The clavicle is grooved on its superior and posterior surfaces in almost its whole length; the groove widens externally (_l_), and contains

*c.* The *precoracoid* (Fig. 34 _cl′_), a slender bar of cartilage, connecting the anterior edge of the scapula with the sternum.

Right shoulder-girdle of _Rana esculenta_, from above.

_ca_ Cav. articularis.
_c c_ Cartilage.
_cl_ Clavicle.
_co_ Coracoid.
_sc_ Scapula.
_sc′_ Suprascapula.
]

Hinder border of the scapula and coracoid, with the connecting cartilage and shoulder-joint, twice nat. size.

_c_ Connecting cartilage.
_d_ Dorsal process.
_co_ Coracoid.
_sc_ Scapula.
_v_ Ventral process.
]

Clavicular cartilage of a young specimen of _Rana esculenta_, enlarged to the adult size.

_c_ Connecting cartilage.
_e_ Epicoracoids.
_c′_ Ligament between the two cartilages.
_cl_ Clavicle.
_cl′_ Clavicle and precoracoid.
_co_ Coracoid.
_co′_ Cartilage of same.
_es_ Omosternum.
_hs_ Sternum proper.
]

*Cartilages* of the shoulder-girdle (Figs. 24, 32, 34). A cartilage (_c_), described by Dugès as the ‘paraglénal,’ connects the scapula with the coracoid, and converts the notch between the two processes (_s_ and _v_) on the inner border of the scapula into an aperture opening posteriorly into the glenoid cavity, and which is filled up by the lining cartilage. This cartilage connects the two processes with the coracoid; being thicker between this and the _proc. coracoideus_, it takes an important share in the formation of the floor of the glenoid cavity. At the outer extremity of the clavicle the cartilage projects and is then continued in the groove on this bone towards the middle line (Figs. 32, 34), where it widens out, and is united by its external margin with the sternum, thus forming the precoracoid as already described, see p. 40. These connections are best seen in young animals, as is shown in Fig. 34.

The clavicle (_cl_) is of ossifying cartilage; the cartilage (_c_), the epicoracoid, is very large, and hyaline, and at _cl_ runs directly into the epicoracoids, which are here united mesially by ligament. In the fully developed animal the whole of the epicoracoid changes to calcified cartilage, as also does the precoracoid lying in the groove of the clavicle.

B. BONES OF THE FORE LIMB.

*1.* The *arm* has but one bone.

Fig. 35. Fig. 36. Fig. 37.

Humerus of _Rana Humerus of _Rana, Humerus of _Rana
esculenta_, female, esculenta_ male, esculenta_, female,
seen from below. seen from below. outer side.

Figures twice natural size.

_c_ Anterior extremity. _c_′ Posterior extremity. _cd_ Crista deltoidea. _cm_ Crista medialis. _t_ trochlea.]

The *humerus*, _os humeri_ (Figs. 35, 36, 37). The shaft of the humerus is, on the whole, cylindrical, the middle part being the narrowest; its dorsal surface is slightly concave, the ventral surface convex. In the upper half the cylindrical form is indistinct, from the presence of a well-marked crest (_crista deltoidea_) upon the under or ventral surface. The hinder half of the bone has very different shapes in the two sexes: in the female it remains cylindrical as far as the elbow-joint; in the male, on the posterior surface, where the _crista deltoidea_ ceases, a marked ridge (_crista medialis_) arises, which gradually winds inwards and terminates at the inner condyle. This sexual difference is found in all the three species described in the Introduction, and it would seem that this ridge increases in height during the pairing season. The muscle which arises from this process is the _flexor carpi radialis_ (Fig. 74 _Fc_), and it attains, in the males, a very large size at the same period; indeed, it is at its origin twice as broad as in the female. Dugès[35] has incorrectly stated that this _crista_ is a peculiarity of _Rana temporaria_, and is wanting in _Rana esculenta_. Pouchet[36] first observed that it was a sexual distinction.

[Footnote 35: _l. c._, p. 68.]

[Footnote 36: Compt. rend. vol. XXV, 1847, p. 761.]

The anterior articular extremity presents a rounded head, which is somewhat flattened externally. The inferior ventral border is sharp, and developed into the above-mentioned bony crest (_crista deltoidea_); the free border is arched and curved outwards. Above, on the outer surface of the head, is found an eminence which may be a rudimentary _tuberc. maius_. The inner half of the head is articular.

The posterior articular extremity consists of a rounded head (_c′_), attached to the posterior extremity of the shaft; internal to this is a small _trochlea_ (_t_), placed upon the inner condyle. The external condyle is but small. The head is embraced by these condyles. Upon the under surface, above the head, is the _fossa cubitalis anterior_. The structure of the two articular extremities of the humerus differs; the upper, as in long bones generally (see page 16), consists of hyaline cartilage surrounded by calcified cartilage, which again is covered by hyaline articular cartilage; the lower extremity is composed of spongy bone, with roundish marrow spaces, and for the most part covered by a layer of calcified cartilage.

The *shoulder-joint*. The socket is formed by the posterior border of the scapula, by both the processes of that bone, the outer portion of the coracoid, and besides these by cartilage, which forms the articular surface already described (Fig. 33). In the macerated bone the floor of the socket opens dorsally into a fossa between the processes of the scapula (Fig. 32). This opening, in the natural condition, is closed by synovial membrane only; the cartilage covering the rest of the space being absent (the sac may easily be inflated, either from the joint itself or through the opening). The margin of the socket consists of a _labrum_, partly fibrous and partly cartilaginous, which is easily removed entire. The capsule, which is attached beneath the _caput humeri_, arises from this. From the articular cartilage of the ventral margin of the socket, and from the adjacent part of the scapula, proceeds a strong band, which is inserted into the flattened outer surface of the head.

*2.* The *forearm*.

Radio-ulnar of the right side of _Rana esculenta_, twice nat. size.

_r_ Radius.
_r_′ Capitulum radii.
_u_ Ulna.
_u_′ Olecranon.
]

The *radio-ulnar*, _os antibrachii_ (Fig. 38). The two bony elements of the forearm are fused into one, which, however, shows traces of its compound character. Of these two bones, that which forms the inferior (in man anterior) border is the radius, the other the ulna. The relative positions of the bony elements are such that they appear to be in a state of semi-pronation; by this the thumb-border of the arm is directed downwards (in man forwards). The two bones so united form a flattened, tube-like bone, the grooved surfaces of which are directed inwards and outwards respectively; the borders being dorsal and ventral. The shaft of the bone is narrower above, becoming gradually wider below. In the upper half, the groove showing the line of junction of the two bony elements is scarcely visible, and it appears as though this part consisted of ulna alone, the radius not reaching so far; below the groove is more marked. The upper articular extremity appears to consist of an _olecranon_ (Fig. 38 _u′_) and a _processus coronoideus_ (_r′_), between which is the greater sigmoid cavity (_cavitas sigmoidea major_) for the _processus cubitalis humeri_. A more careful examination shows this to be incorrect: the portion of the concave articular surface, which lies in the immediate neighbourhood of the ventral border, undoubtedly represents the articular surface of the _capitulum radii_, and the upper portion of the articular surface (at _u′_) belongs to the _ulna_ and articulates with the _trochlea_ (Figs. 35, 36 _t_) of the humerus. The inner border of the upper extremity of the bone articulates with the groove _t_ of the humerus. The inferior extremity forms one of the usual cartilaginous epiphyses, enclosing the two bones. That part of the extremity corresponding with the radius is triangular and convex, it is prolonged upon the inner or under surface of the bone by means of a process; the ulnar portion of the bone forms a _capitulum_. The structure of the inferior extremity is that of epiphyses in general, except that there are two medullary cavities in a common sheath of calcified cartilage; the anterior head consists of cancellous tissue, with a covering of calcified cartilage.

*3.* Bones of the *hand* (Fig. 39).

*Dugès*, Pl. VIII, Figs. 37, 38, 39, 40, 41, 42, 43, 52.

*a.* Bones of the *wrist*, _ossa carpi_. These are arranged in two rows, proximal and distal. The proximal or anterior row has three bones, viz.:--

1. _Os lunatum_, the middle bone (Fig. 39 _l_), Dugès, n. 38, articulates with the radial part of the articular surface of the radio-ulnar by a concave surface; with the large bone of the second row (_hc_) it articulates by means of a rounded head; and with the two other bones of this row, _os naviculare_ (_n_) and _pyramidale_ (_p_), with the former by a saddle-shaped surface, with the latter chiefly by ligament. The bone is irregularly cuboid; the dorsal and palmar surfaces are non-articular. With Dugès I regard this bone as _os lunatum_; Mertens[37] regards it as _os naviculare_.

[Footnote 37: Mertens, _l. c._]

Bones of the forearm and hand of _Rana esculenta_, right side, dorsum, twice nat. size.

_a_ Os antibrachii.
_hc_ Os capitato-hamatum.
_l_ Os lunatum.
_m_ Ossa metacarpi.
_n_ Os naviculare.
_p_ Os pyramidale.
_r_ Radial portion of the radio-ulnar.
_t_ Os multangulum majus or trapezium.
_t′_ Os multangulum minus or trapezoides.
_u_ Ulnar portion of the radio-ulnar.
_I_-_V_ First to fifth fingers, the fifth only
of os metacarpi, the second and third of
two, fourth and fifth of three phalanges.
]

2. _Os pyramidale_ (Fig. 39 _p_), Dugès, n. 37, articulates with the ulnar part of the posterior articular extremity of the radio-ulnar. Anteriorly the bone has a facet which receives the _capitulum ulnae_, and alongside this a small flat surface which articulates with the radius. Posteriorly, opposite to the second row, it presents a long raised articular surface, extending from the dorsum to the palmar surface; and on the palmar aspect of the bone is a ridge running from before backwards. Mertens names this bone _os lunatum_.

3. _Os naviculare_ (Fig. 39 _n_), Dugès, n. 39. The third bone of the first row does not articulate with the bones of the forearm. It is connected with the _os lunatum_ by a saddle-shaped surface, posteriorly with the _os capitatum_ by means of a concave surface. On the inner surface is a small concave articular facet for the _os multangulum minus_ or _trapezoides_ (Fig. 39 _t′_). The convex palmar surface of the bone articulates with the _os multangulum majus_ (_t_); the radial side is non-articular, and with the _os lunatum_ forms a ridge directed forwards. Mertens names this bone _os triquetrum_. It is evident, however, that if the arrangement in man obtains as a standard, the nomenclature of Dugès, which I have here used, is correct; but the _os naviculare_ is no longer in contact with the articular surface of the _os antibrachii_.

The second or distal row also consists of three bones:--

4. _Os capitato-hamatum_ (Fig. 39 _hc_), Dugès, n. 40, 41, 42, corresponds with the _os capitatum_ and _hamatum_[38], which are here fused together. It is the largest bone, and articulates with all three bones of the first row; it is crescentic, with the concavity directed posteriorly, and on the convex surface has three facets for the three outer _ossa metacarpi_.

[Footnote 38: Dugès thinks that _os trapezoides_ is also included.]

5. _Os multangulum minus_, _s. trapezoides_ (Fig. 39 _t′_), Dugès, n. 43, is a small bone lying next to the foregoing; it articulates with the _os metacarpi II_, and anteriorly with the _os naviculare_. Dugès considers it to be the _os trapezium_.

6. _Os multangulum majus_, _s. trapezium_ (Fig. 39 _t_), is a small bone, which is placed on the convex palmar auricular side of the _os naviculare_. Dugès regards this bone as _os metacarpi pollicis_ (Dugès, n. 44), Mertens as _multangulum minus_. It appears to me that the interpretation here given is justified, because it articulates with the rudiment of the thumb, and as it possesses no resemblance to a long bone it cannot be regarded as an _os metacarpi_.

*Structure of the carpal bones.* All the carpal bones consist of calcified cartilage, though variations due to age occur in the amount of the deposit.

*Wrist joint.* As stated above, the _os lunatum_ and _os pyramidale_ are articulated with the forearm. In addition to the capsules uniting the parts, there are strengthening ligaments, two of which require special mention. One of these arises from the palmar surface of the posterior extremity of the ulna, and passes to the sharp palmar ridge of the _os pyramidale_, where it is attached, and is inserted into the _os capitato-hamatum_; the second ligament passes in a similar manner on the palmar surface from the radius to the _os naviculare_. Between the two ligaments there is on the volar surface a deep excavation.

Bones of the forearm and hand of _Rana esculenta_, right side, dorsum, twice nat. size.

_a_ Radio-ulnar.
_hc_ Os capitato-hamatum.
_l_ Os lunatum.
_m_ Ossa metacarpi.
_n_ Os naviculare.
_p_ Os pyramidale.
_r_ Radial portion of the radio-ulnar.
_t_ Os multangulum majus or trapezium.
_t′_ Os multangulum minus or trapezoides.
_u_ Ulnar portion of the radio-ulnar.
_I_-_V_ First to fifth fingers, the first only
of a metacarpal, the second and third of
two, fourth and fifth of three phalanges.
]

*Movements* of the hand. The two bones of the forearm being firmly united, pronation and supination, as in man, are impossible. The normal position, as already remarked (see radio-ulnar), is that of semi-pronation (compare Figs. 2 and 74). If the animal be in its natural posture, with the arm bent at the elbow (Fig. 1) it can touch the ground with the ulnar border only; but when the whole surface of the hand rests upon the ground, the action is brought about as follows: the plane of the carpus is in extension parallel with that of the forearm; in flexion, almost at right-angles with that plane (Fig. 74) The _os lunatum_ glides on the prolongation of the articular surface on the inner palmar surface of the radius, while the _os pyramidale_ is held firmly by the ligament just described. The hand follows the movement of the _os lunatum_, and at the same time the three outer _ossa metacarpi_ gliding with it inwards, the fingers of the hand turn inwards.

*b.* The Bones of the *metacarpus*, _ossa metacarpi_ (Fig. 40 _m_). Of these there are five: the *second* to the *fifth* are of about equal length; the first, forming the rudiment of the thumb, hidden beneath the skin, is much shorter. This metacarpal bone of the *thumb* is regarded by Dugès and others as the first phalanx. My reason for describing it as a metacarpal has already been given. This bone also presents differences in the two sexes. Meckel’s[39] observation that it exists only in the male is incorrect; it is a large, broad and sickle-shaped mass of calcified cartilage or even true bone, while in the female it is simply a small cartilaginous rod; as this almost entirely disappears in dried specimens, Meckel’s statement is explained. The *second* finger has in the frog assumed the functions of the thumb, and, in the males, in the breeding season swells and undergoes an essential alteration of structure. The metacarpal of this finger also displays differences in the sexes, being in the male stronger, broader, and on the inner side provided with a spine-like prolongation, for the tendon of the _abductor digiti II (pollicis) longus_, which attains an unusual development during the breeding season. The remaining metacarpal bones, the *third*, *fourth*, and *fifth*, are of similar form, the last being provided with a tubercle. The anterior articular extremities are rather broad and concave, and the posterior have rounded heads.

[Footnote 39: _l. c._, II, 464.]

*c.* The *phalanges*, _phalanges digitorum_. The hand has four fingers and the rudiment of a fifth, which latter is completely hidden under the skin, and as already explained, consists of a metacarpal only. Of the four fingers, the fourth is the longest, the third the shortest, the second and fifth of intermediate and about equal length; the fourth and fifth fingers have each three phalanges, the second and third have each two. Their shape is not unlike that of the human phalanges.

V. THE BONES OF THE HINDER EXTREMITY.

A. BONES OF THE PELVIC GIRDLE (Fig. 41).

The *pelvis* has a characteristic V-shape, the pubic and ischiatic bones of the two sides together forming a vertical plate (_a p_), which divides anteriorly into the two iliac bones (_il_). The pubic and ischiatic bones being united by their median surfaces, one can only speak of the pelvic cavity as the space between the two ilia.

*1.* The *ilia*, _ossa ilii_ (Fig. 42 _il_). In these a broader part or body can be distinguished, which takes part in the formation of the _acetabulum_ (_a_). The hinder and broadest part of the bone is joined to the corresponding portion of its fellow by ligament; anteriorly the two diverge, bounding a cone-shaped cavity, the pelvis. The suture, by which the body of the iliac bone is united with the ischiatic and pubic bones, runs from above downwards through the middle of the _acetabulum_ (Fig. 42, from _p_ through the _acetabulum_ to _is_). Inferiorly and in front the united _ilia_ form a prominence (_s_), which represents the _symphysis oss. pub._ of man. The expanded portions of the ilium rest directly over the articular cavity by means of a somewhat constricted part or root. The _ala_ is a sabre-like bone, with the sharper, more convex border directed upwards; the more concave, thicker border downwards. The two surfaces, of which the inner is grooved, are directed respectively inwards and outwards. The broader part of the blade springs directly from the neck or root (at _il′_), and at this end of the sharp convex border is a process, _process. sup._, from which the tendon of the _m. vastus externus_ arises. The anterior end of the blade is a hollow cylinder, containing cartilage, movably articulated to the transverse process of the last vertebra or sacrum.

Pelvis of _Rana esculenta_, from below, nat. size.

_a_ Acetabulum.
_il_ Iliac bone.
_p_ Pubic bone.
]

Pelvis of _Rana esculenta_, left side, twice nat. size.

_a_ Acetabulum.
_d_ Upper sharp border.
_il_ Iliac bone.
_il′_ Superior process.
_is_ Ischium.
_is′_ Tuber ischii.
_p_ Os pubis.
_s_ Inferior process of the ilium.
_v_ Lower border of same.
]

*2.* The *ischia*, _ossa ischii_ (_is_), are irregular, four-cornered plates of bone, united together by the whole extent of their inner surfaces. The vertical plate formed by the union of the two bones takes only a very small share in the formation of the articular cavity. Above, it has a somewhat sharp border, continued with the ilium into a process (_is′_) corresponding with the united _tubera ischii_; the hinder border, which is united below with the pubic cartilage, is curved.

Horizontal section through the iliac, pubic, and ischiatic bones.

_a_ Acetabulum.
_il_ Ilium.
_is_ Ischium.
_p_ Pubic cartilage.
_s_ Ligaments which unite the bones of opposite sides.
]

*3.* The *pubes*, _os pubis_ (Figs. 41, 42, 43 _p_). Ossified pubic bones do not exist; even in old animals they are composed of calcified cartilage. Each is a triangular cartilage, wedged between the ilium and ischium, but also taking part in the formation of the _acetabulum_. The pubes of opposite sides are, as shown in section in Fig. 43, united by ligaments in the median plane.

B. BONES OF THE HIND-LIMB.

*1.* The *thigh*.

The *femur*, _os femoris_ (Fig. 44). The shaft is cylindrical, with a slight double or S-shaped curve. In the anterior portion the convexity is directed upwards, in the two hinder thirds downwards. Towards the hinder extremity it is flattened from above downwards. The anterior extremity is a rounded articular head placed directly on the shaft like that of the _humerus_. This head is somewhat flattened from side to side; and in structure resembles that of the humerus. The inferior extremity is rounded below, but flattened above (towards the hollow of the knee) and behind.

*Hip-joint.* The articular cavity is deepened by a fibrous ring, _labrum cartilagineum_, which fits closely upon the _caput femoris_; from this _labrum_ the joint-capsule arises, to be inserted behind the head; close to the lower border of the cavity a _ligamentum teres_ arises, which is inserted into the _caput femoris_.

*2.* The *leg*.

Femur of _Rana esculenta_, right side, twice nat. size.

_a_ Anterior extremity.
_p_ Posterior extremity.
]

*Tibio-fibula*, _os cruris_ (Fig. 45). This consists of a single bone, the _os cruris_; it is often called the _tibia_, but presents, however, distinct indications of being formed of two bones, the _tibia_ and _fibula_. The shaft is not quite straight; it is thinner in the middle and flattened from above downwards. On the upper as also on the lower surface of the bone is a groove, passing from the middle towards each extremity; this deepens as it proceeds, and is an indication of the compound nature of the bone. In the middle of each surface of the bone is the opening of a canal, through which a bristle may be passed: the canal has bony walls. The medullary cavity is, for the most part, double, being single only in the middle. The anterior extremity is articular, and presents a median groove, which is prolonged on to the under surface. The posterior extremity forms a transverse condyle, which has at its inner part a notch for the tendon of the _m. tibialis posticus_.

Tibio-fibula of _Rana esculenta_, twice nat. size, seen from below.

_a a_ Grooves.
_f_ Foramen nutritium.
_t_ Anterior articular extremity.
_t′_ Posterior articular extremity.
_t″_ Groove on malleolus internus for tendon of _m. tibialis posticus_.
]

The *knee-joint* consists of a capsule strengthened by the insertions of numerous tendons. Within this the articular surfaces of the _femur_ and tibio-fibula are connected by means of fibro-elastic bands, which spring from the latter bone and cross each other, thus representing the _lig. cruciata_. The articular surfaces are moreover deepened by loose semilunar cartilages, corresponding with the inter-articular cartilages of the knee-joint of man. In addition, on either side of the joint, are found auxiliary ligaments.

Section of the tibio-fibula through the under extremity.

_a_ Cartilaginous epiphysis.
_m_ Marrow cavities.
_t″_ Connecting mass.
_t t′_ The two cylinders of bone.
]

*3.* The *foot* (Fig. 47).

*a.* The *ankle*, _ossa tarsi_. The *tarsus* consists of two rows of bones.

α. The *proximal row* consists of two long tubular bones (Fig. 47 _ac_), which are parallel to each other, and undoubtedly correspond with the *astragalus* (_talus_) and *calcaneum*. The bones are separated in the middle, but approach each other at either end. The outer of these bones (_c_) I have named calcaneum, following Cuvier and Dugès; the inner, astragalus (_a_). The two bones are surrounded and enclosed at their anterior and posterior extremities in a common epiphysis of calcified cartilage, which has the usual structure found elsewhere. The _ligamentum calcanei_, which will be described below (see Muscles of Foot, Fig. 88 _lc_), may be regarded as an unattached process of the heel[40].

[Footnote 40: Meckel, _l. c._, II, p. 488, regards the cartilage in the _tendo Achillis_ as such.]

β. The *distal* row of the tarsals are all composed of calcified cartilage. They are:--

1. _Os cuboideum_ (Fig. 47 _cb_), a flat plate of cartilage, concave in front, convex behind, placed between the common epiphysis of the astragalus and calcaneum (_ac_) and the _ossa metatarsi II_ and _III_. This corresponds, as Dugès suggests, with the separated _os cuboideum_ and _cuneiforme III_ of other batrachians, _e. g._ Bufo.

2. On the inner side of the above, between the _astragalus_ and _metatarsus I_ lies a small body, concave in front, convex behind, which we may regard, with Dugès, as the analogue of the _os naviculare_ (Fig. 47 _n_).

Right foot of _Rana esculenta_, palmar surface, twice nat. size.

_a_ Astragalus.
_ac_ Common epiphysis.
_c_ Calcaneum.
_cb_ Os cuboideum.
_h_ First, _h′_ second cartilage of supplemental toe.
_m_ Ossa metacarpi.
_n_ Os naviculare.
_I_ to _V_ First to fifth toe.
]

3. This latter supports a cartilage which forms a projection on the inner border, covered with skin. This consists of closely-united pieces, a small round, basal piece (_h_), and a flattened beak-like piece (_h′_). Dugès considers these pieces as the first and second _ossa cuneiformia_; I rather incline to Meckel’s opinion that they represent a rudimentary hallux, the first being the _os metatarsi_, the second a _phalanx_. Both are composed of calcified cartilage; in _R. temporaria_ the lime-deposit seems to be less than in _R. oxyrhinus_ and _R. esculenta_, and the projection consequently softer[41].

[Footnote 41: In the text these two cartilages are termed the ‘supplemental toe.’]

*b.* The *metatarsal bones*, _ossa metatarsi_ (Fig. 47, _m_ _I_-_V_). The five _ossa metatarsi_ are long, thin tubular bones, the anterior articular extremities of which are broader above and narrow below, hence are wedge-shaped, and anteriorly present flat surfaces for articulation with the _tarsus_. The shafts are long and thin; the posterior extremities have rounded heads. The comparative length of these is as follows: the fourth is the longest, then come the third, fifth, second, and first in order. In structure they resemble other tubular bones.

*c.* The *phalanges*, _phalanges digitorum_ (Fig. 47). The total lengths of the separate toes correspond with that of the _ossa metatarsi_, but the distinctive differences are increased, partly by the difference in number and partly by the varying lengths of the phalanges. The first and second toes have each only two phalanges, the third and fifth have each three, the fourth, which is the longest, has four. The terminal phalanges are somewhat hooked towards the plantar surface.