u nn nn, 
26 
Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 
Brain, and Cephalic Nerves 
nn nn. 
Hypophysis and Infundibulum 
21 
22 
23 
24 
25 
26 
Cranio-caudal axis of fore-brain a little greater than vertical. A shallow recessus neuroporicus present. Skin and 
neurectoderm fused for I8 u (by sections), in median line, anterior to recessus. Distinct recessus postopticus and 
|recessus praeopticus. Mid-brain a little dilated ; broader ventrally than dorsally; separated from fore-brain externally 
by shallow lateral grooves. Roof of hind-brain composed of a single layer of columnar cells. Lateral walls much 
thickened, with as many as six rows of nuclei in thickest part. At ae of trigeminus, ventricle kite-shaped in 
cross section, in region of otocyst and posteriorly, hour-glass-shaped in cross section. — Connection between 
|trigeminal crest and urtrochlearis more slender and irregular in outline. Ophthalmic portion of trigeminal crest 
|lies in groove between optic vesicle and fore-brain; fused with skin ectoderm above optic vesicle; connected with 
|the small thalamic crest by a slender strand, one cell thick. Facial and acoustic ganglia differentiated. Facial crest 
‚extends down dorsal half of second gill arch. Glossopharyngeal crest disconnected from both vagus and facial 
erests; extends down dorsal half of third gill arch. Anterior end of vagus crest much enlarged ventrally; divided 
into first and second branchial branches. A blunt process extends backward 30 u from ventral posterior angle. 
Crest broadly continuous with spinal nerve crest dorsally. 
Axis of fore-brain bent a little caudal from that of mid-brain. Skin and neurectoderm fused for nearly 70 u. along 
median line at anterior neuropore. Very shallow recessus praeopticus and recessus postopticus. Beginning of 
tuberculum posterius? Mid-brain bent almost at right angles to hind-brain. Almost circular in cross section. 
Lateral walls of hind-brain very much thickened. Ventral half of canal reduced to a narrow slit between them. 
Ventral expansion of canal entirely absent anterior to otocyst, — very slight behind otocyst. — Thalamic crest 
disconnected from trigeminal. Urtrochlear connected with trigeminal crest by a broad band on the right, and a 
very small one on the left side. Distinct thickening of trigeminal crest above optic vesicle (anlage mesocephalic 
ganglion). Epibranchial and dorso-lateral placodes of facial established. Dorso-lateral placodes of glossopharyngeus 
and vagus established. 
Cranio-caudal and vertical diameters of fore-brain about equal. Shallow recessus praeopticus and recessus post- 
opticus. Mid-brain separated externally from fore- and hind-brain by well defined but shallow grooves. Walls, 
floor, and roof of mid-brain of equal thickness. Hind-brain approximately four times as long as broad. Greatest 
transverse diameter in region of otocyst. Lateral walls, at origin of trigeminus, flattened until lying almost in 
transverse plane. Slight indication of division into dorsal and ventral zones in this region. Floor plate a single 
layer of elongated cells. No ventral enlargement of canal anterior to origin of vagus. — Urtrochlear and thalamic 
crests completely separated from trigeminal. Urtrochlear crest present in four sections of 6 » only. Trigeminal 
crest attached to middle third of medullary tube; expanded above optic vesicle; extends down dorsal half of mandi- 
bular arch. A long slender strand of Sans (urtrochlear process) extends forward and upward from anterior edge 
of trigeminal crest, towards urtrochlear crest. Epibranchial placode of glossopharyngeus established. 
Vertical diameter of fore-brain vesicle approximately three-fouıths of cranio-caudal. In the median line, floor and 
roof of about equal thickness. Lateral walls approximately twice as thick as floor or roof. A very shallow recessus 
neuroporicus. Brain wall and skin ectoderm in contact, but not fused, in front of recessus. Recessus praeopticus 
and recessus postopticus barely distinguishable at median line. Distinct recessus mammillaris. Tuberculum posterius 
|appears, at the median line, as a broadiy U-shaped fold of the floor of the fore-brain. Roof of hind-brain widely 
|expanded — composed of a single layer of squamous cells. Lateral walls very much thickened and in otic region 
almost in contact. A very narrow peripheral layer of ectoglia ventral to origin of trigeminus. — Thalamic crest 
entirely absent. No connection between urtrochlear and trigeminal crest. Trigeminal crest constricted into an 
anterior (ophthalmic) and a main posterior portion. Slender urtrochlear process. Mesocephalic ganglion lies over 
| optic cup, — increased in size in comparison to preceding stage. Facial crest extends ventrally to middle of hyoid 
arch, as do glossopharyngeal and first and second branches of vagus crest. Third branch of vagus crest extends 
ventrally into dorsal end of sixth branchial arch. Epibranchial placodes of first and second branches of vagus 
crest established. 
Cranio-caudal diameter of telencephalon about an eighth greater than vertical. 
| Distinct recessus praeopticus — brain wall thickened cranial to it. 
wall thickened between it and recessus praeopticus. 
ceding stage — in mid-sagittal section shaped like a 
bulum. Diencephalon broadly oval in cross section, 
No distinct recessus neuroporicus. 
Shallow, indistinet recessus postopticus. Brain 
Tuberculum posterius a little more prominent than in pre- 
much flattened W. For processus mammillaris see infundi- 
— lateral walls nearly twice as thick as roof or floor. Distinct 
velum transversum — V-shaped in section. Distinct but small, post-velar arch and pinealis, the latter directed 
eg Mid brain broadiy oval in cross section — floor and walls twice as thick as roof. A shallow sulcus 
imitans, extending from anterior of origin of trigeminus to origin of facial nerve, and from the middle of otocyst 
region to origin of en ker irn nerve — absent in anterior half of otocyst region. Formation of cinerea 
beginning throughout length of myelencephalon. Narrow peripheral layer of ectoglia in ventral zone. — Urtrochlear 
crest entirely absent. Terminal nerve represented by a few cells connecting fore-brain with nasal epithelium? 
Oculomotor nerve extends backward to mesocephalic ganglion. Long slender urtrochlear process of trigeminus. 
| Distinet mesocephalic ganglion. The two above structures connected with trigeminal ganglion by slender ganglionic 
cord. Short mandibular and maxillary rami ot trigeminus. Slight differentiation of acoustic, hyomandibular, and 
superficial ophthalmic portions of facial-acoustic ganglion. Short buccal and superficial ophthalmic rami — placodes 
| of each established. Epibranchial placode of facıal nerve established. Hyoid ramus of facial nerve in dorsal third 
of hyoid arch. Dorso-lateral and epibranchial placodes of glossopharyngeus established. First, second, and third 
branchial rami of vagus. Epibranchial and dorso-lateral placodes of each formed. Lateral ramus extends backward 
a little beyond posterior end of pharynx. 
Telencephalic vesicle enlarged and elongated, as compared with preceding stage. 
twice vertical. A distinct though shallow recessus neuroporicus present. 
shaped in cross section, shallow at median line. Recessus opticus distinguishable only at median line. Velum 
transversum twice as long (Ioo u) at the median line as in preceding stage (No. 24); epithelial walls in contact. 
Distinct post-velar arch. Pinealis extends backward slightly over roof of diencephalon. — Urtrochlear process of 
trigeminal ganglion absent. Anlage of ciliary ganglion attached by a few strands to distal end of oculomotor 
nerve, and by a broad cellular cord to mesocephalic ganglion. 
Cranio-caudal diameter nearly 
Recessus praeopticus laterally deeply V- 
Vertical diameter of telencephalon three-fifths of cranio-caudal. Lateral walls of telencephalon over twice as thick 
as floor. Floor twice as thick as roof. No distinct recessus neuroporicus. Recessus praeopticus shallowly V-shaped 
at the median line — walls much thickened anterior and posterior to it. A very narrow peripheral band of ectoglia 
just posterior to recess. Velum transversum 300 u in length at median line, a thin layer of mesenchyma between 
epithelial walls. Superior commissure represented by a narrow peripheral band of ectoglia just anterior to pinealis. 
| Pinealis 120 u in length at median line. Posterior commissure a broad peripheral layer of ectoglia. Ventral zone 
of lateral walls of mesencephalon a little thickened. A narrow ectoglic layer at base of ventral zone. Anlage of 
cerebellum a distinet thickening of roof or anterior end of hind-brain. Broad shallow sulcus limitans, extendin 
entire length of hind-brain. Distinct formation of cinerea ventral to origin of trigeminal and facial nerves. Broa 
| band of ectoglia on either side of floor plate throughout length of hind-brain. Distinct sensory bundles of trigeminal 
jand facial nerves. — Olfactories established. Deep ophthalmic ramus of trigeminus extends forward nearly to ventral 
|edge of optic cup. Mesocephalic BANENIER much larger. Connected on its mesial surface, by a few cellular strands, 
|with a very small ciliary ganglion. Connected by a broad cellular band with trigeminal 'ganglion, — superficial 
| ophthalmic ramus of trigeminus a small branch arising from the anterior surface of this band. Superficial ophthalmic 
|ramus of facial extends forward a little beyond anterior edge of trigeminal ganglion. Three branchial rami of 
| vagus — fourth forming. Visceral ramus of vagus extends posteriorly to anterior end of oesophagus. Lateral 
line ramus extends backward to middle of cardiac region. 
Ventral surface of fore-brain in contact 
with thickened hypophyseal plate of epi- 
thelium. No invagination of hypophysis. 
Hypophyseal plate in contact with brain 
wall at median line, from recessus prae- 
opticus nearly to tuberculum posterius. Pos- 
terior (upper) end invaginated, forming a 
shallow pocket, the cranial end of which 
is in contact with tip of notochord. 
Posterior (upper) end of hypophysis extends 
forward from mouth 48 u (by sections). 
Triangular in cross section. In contact with 
floor of fore-brain anteriorly, and with walls 
of lateral chambers of premandibular somite 
laterally. 
Small but distinct recessus mammillaris and 
tuberculum posterius. Hypophysis in con- 
tact with brain wall from posterior wall of 
mammillary recess forward nearly to re- 
cessus praeopticus. Cranial wall in contact 
with median stalk of premandibular somite. 
Posterior, i. e. invaginated part, of hypo- 
physis 0.2 mm. in length at median line. 
Expanded distally. Anterior part extends 
forward to recessus postopticus. 
Recessus mammillaris slightly recurved 
above tuberculum posterius. In contact 
anteriorly with median stalk of premandi- 
bular somite; posteriorly, with distal ex- 
tremity of hypophysis. Invaginated (pos- 
terior) portion of hypophysis approximately 
0.3 mm. in length. Anterior wall nearly 
twice as thick as posterior. 
Recessus mammillaris recurved a little dor- 
sal to tuberculum posterius. Recessus in- 
fundibuli a very shallow depression in floor 
of infundibular region, caudal to recessus 
mammillaris. Posterior part of hypophysis 
approximately 0.4 mm. in length. Trans- 
verse diameter of proximal end of sac two- 
thirds that of distal. Walls in contact at 
proximal end. 
