Chapter III: Part 3

In front of the coraco-arcuales communes are three large longitudinal muscles. The median, unpaired one, arising from the fascia between the coraco-arcuales communes and inserted upon the posterior surface of the lower jaw, is the _coraco-mandibularis_. The other two, which lie dorsal to and outside of the coraco-mandibularis, are the _coraco-hyoidei_. They arise from the fasciae covering the anterior ends of the coraco-arcuales communes and posterior parts of the coraco-branchiales, and insert upon the basihyal.

Dissect out the coraco-mandibularis and coraco-hyoidei, noting particularly the form and place of origin of the latter. Dorsal to the coraco-hyoidei are the first divisions of the right and left _coraco-branchialis_ muscles, which arise from fascia covering the anterior ends of the coraco-arcuales communes, and are inserted upon the ventral extremity of the ceratohyal cartilage. Notice that they pass dorsad to the anterior branches of the aorta, and that the aorta itself can be exposed between them.

Remove the coraco-arcualis communis by dissecting it from the pectoral girdle and reflecting it forward. The other four divisions of the coraco-branchialis are now revealed, attached to the lateral surface of the pericardium and the lateral portion of the coracoid. The divisions of the muscle are clearly separated only near their insertions. The second, third, and fourth coraco-branchials are attached to the hypobranchial cartilages of the second, third and fourth visceral arches. The fifth division is inserted upon the lateral portion of the basibranchial and the expanded medial end of the fifth ceratobranchial.

_The first_ aortic branch passes ventral to the first coraco-branchial. _The second_ aortic branch passes between the first and second coraco-branchials. _The third_ aortic branch passes between the second and third coraco-branchials. _The fourth_ aortic branch passes between the third and fourth coraco-branchials.

Expose the dorsal ends of the gill arches by clearing away muscles and other tissues between the gill pouches and the spinal column. Two sets of four small muscles (interarcuales) will be found connected with the branchial cartilages. The second, third and fourth _medial interarcuales_ extend from the posterior surfaces of pharyngo-branchial cartilages 1, 2, and 3, to the dorsal surfaces of pharyngo-branchials 2, 3, 4, and 5. The first medial interarcuale arises from the under surface of the cranium and inserts on the upper end of the first pharyngo-branchial.

The _lateral interarcuales_ lie immediately below the medials. The first has a double origin, most of the fibres arising from the lower part of the posterior edge of the first pharyngo-branchial; a smaller bundle from the anterior edge of the second pharyngo-branchial. Its insertion is along the dorsal surface of the first epibranchial cartilage. The second and third lateral interarcuales are like the first, but since the fourth and fifth pharyngo-branchials are fused, the origin of the fourth lateral interarcuale is not divided.

The circular muscles of the oesophagus are strongly attached to the last pharyngo-branchial.

MUSCULATURE OF THE PECTORAL FIN. The dorsal muscle of the fin (_levator-retractor_) arises mostly from the scapular portion of the girdle, with a small part arising from the fascia covering the lateral musculature of the body. It is attached in fasciculi to the dorsal surfaces of the cartilaginous rays. The ventral muscle (_depressor-protractor_) arises from the median portion of the girdle and is inserted upon the cartilaginous rays in similar fasciculi. A portion of the lateral body muscles is inserted upon the scapular portion of the girdle.

MUSCULATURE OF THE PELVIC FIN. Ventral surface: An _adductor_ muscle has origin upon the postero-lateral edge of the girdle; it is inserted upon the antero-medial surface of the basal cartilage of the fin. The _depressor_ muscle consists of small fasciculi, each corresponding to a cartilaginous ray. They arise from the postero-lateral surface of the basal cartilage and are inserted upon the distal extremities of the rays.

Dorsal surface: The _abductor_ arises from the fascia covering the trunk muscles, and inserts upon the fascia covering the intrinsic muscles of the dorsal side of the fin. These latter (_levatores_) are arranged in exactly the same manner as the fasciculi of the depressor.

MUSCULATURE OF THE DORSAL FINS. A sheet of muscle is attached to each side of the anterior dorsal fin, extending nearly up to the bases of the dermal fin-rays. This muscle passes downward between the dorsal body musculature of the two sides. Part of the fibres arise from the fasciae covering the medial surfaces of the body muscles, part from the basal cartilage of the fin itself. They are inserted upon the lateral surfaces of the broad cartilaginous fin-rays. The muscles of the posterior dorsal fin are exactly similar in arrangement.

MUSCULATURE OF THE CAUDAL FIN. There is no special musculature for the dorsal portion. A narrow, band-like muscle is found on each side of the ventral portion, widest above the triangular ventral lobe. The fibres of this muscle arise upon the flattened, expanded ends of the haemal spines. They pass obliquely backward and upward to be inserted in the fascia underlying the skin.

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● Transcriber’s Notes:
○ Missing or obscured punctuation was silently corrected.
○ Typographical errors were silently corrected.
○ Inconsistent spelling and hyphenation were made consistent only
when a predominant form was found in this book.
○ Text that was in italics is enclosed by underscores (_italics_).