Chapter IX

DEVELOPMENT OF THE ORGANS IN THE HEAD, pp. 397-445.

DEVELOPMENT OF THE BRAIN, pp. 397-407. General history. _Fore-brain._--Optic vesicles. Infundibulum. Pineal gland. Olfactory lobes. Lateral ventricles. _Mid-brain._ _Hind-brain._--Cerebellum. Medulla.--Previous investigations. Huxley. Miklucho-Maclay. Wilder. ORGANS OF SENSE, pp. 407-412. _Olfactory organ._--Olfactory pit. Schneiderian folds. _Eye._ General development. Hyaloid membrane. Lens capsule. Processus falciformis. _Auditory organs._--Auditory pit. Semicircular canals. MOUTH INVOLUTION and PITUITARY BODY, pp. 412-414. Outgrowth of pituitary involution. Separation of pituitary sack. Junction with infundibulum. DEVELOPMENT OF CRANIAL NERVES, pp. 414-428. Early development of 5th, 7th, 8th, 9th and 10th cranial nerves. Distribution of the nerves in the adult. _The fifth nerve._--Its division into ophthalmic and mandibular branches. Later formation of superior maxillary branch. _Seventh and auditory nerves._--Separation of single rudiment into seventh and auditory. Forking of seventh nerve over hyomandibular cleft. Formation of anterior branch to form ramus ophthalmicus superficialis of adult. General view of morphology of branches of seventh nerve. _Glossopharyngeal and vagus nerves._--General distribution at stage L. Their connection by a commissure. Junction of the commissure with commissure connecting posterior roots of spinal nerves. Absence of anterior roots. Hypoglossal nerve. MESOBLAST OF HEAD, pp. 429-432. _Body-cavity and myotomes of head._--Continuation of body-cavity into head. Its division into segments. Development of muscles from their walls. General mesoblast of head. NOTOCHORD IN HEAD, p. 433. HYPOBLAST OF THE HEAD, pp. 433-434. The formation of the gill-slits. Layer from which gills are derived. SEGMENTATION OF THE HEAD, pp. 434-440. Indication of segmentation afforded by (1) cranial nerves, (2) visceral clefts, (3) head-cavities. Comparison of results obtained.

CHAPTER X.

THE ALIMENTARY CANAL, pp. 446-459.

_The solid oesophagus._--OEsophagus originally hollow. Becomes solid during Stage K. _The postanal section of the alimentary tract._--Continuity of neural and alimentary canals. Its discovery by Kowalevsky. The postanal section of gut. Its history in Scyllium. Its disappearance. _The cloaca and anus._--The formation of the cloaca. Its junction with segmental ducts. Abdominal pockets. Anus. _The thyroid body._--Its formation in region of mandibular arch. It becomes solid. Previous investigations. _The pancreas._--Arises as diverticulum from dorsal side of duodenum. Its further growth. Formation of duct. _The liver._--Arises as ventral diverticulum of duodenum. Hepatic cylinders. Comparison with other types. _The subnotochordal rod._--Its separation from dorsal wall of alimentary canal. The section of it in the trunk. In the head. Its disappearance. Views as to its meaning.

CHAPTER XI.

THE VASCULAR SYSTEM AND VASCULAR GLANDS, pp. 460-478.

_The heart._--Its development. Comparison with other types. Meaning of double formation of heart. _The general circulation._ The venous system. The primitive condition of. Comparison of, with Amphioxus and Annelids. The cardinal veins. Relations of caudal vein. _The circulation of the yolk-sack._--Previous observations. Various stages. Difference of type in amniotic Vertebrates. _The vascular glands._--Suprarenal and interrenal bodies. Previous investigations. _The suprarenal bodies._--Their structure in the adult. Their development from the sympathetic ganglia. _The interrenal body._--Its structure in the adult. Its independence of suprarenal bodies. Its development.