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.