430 THE DEVELOPMENT OF THE CHICK 
posterior region of the otic capsule expands dorsally above the 
hind-brain, and forms a bridge of cartilage extending from one 
capsule to the other, known as the tectum synoticum (Fig. 244, 
33). (3) The preotic region expands laterally and dorsally in 
the form of a wide plate (alisphenoidal plate) which is expanded 
transversely, and thus possesses an anterior face bounding the 
orbit posteriorly and a posterior face forming part of the anterior 
wall of the cranial cavity. This plate arises first between the 
ophthalmic and maxillo-mandibular branches of the trigeminus, 
and subsequently sends a process over the latter that fuses with 
the anterior face of the otic capsule, thus establishing the foramen 
prooticum. 
For an account of numerous lesser changes, the student is referred 
to Gaupp (1905), and the special literature (especially Parker, 1869). 
The various foramina for the fifth to the twelfth cranial nerves are 
defined during the process of chondrification; the majority of these are 
shown in the figures. 
The trabecular region may be divided into interorbital and 
ethmoidal (nasal) regions. The basis of the skeleton in this 
region is formed by the trabecule already described. The median 
plate formed by fusion of the trabeculee extends from the pituitary 
space (fenestra hypophyseos) to the tip of the head; a high median 
keel-like plate develops in the interorbital and internasal regions 
Fig. 243. — Skull of an embryo of 65 mm. length; right side. Membrane 
bones in yellow. Cartilage in blue. (Drawn from the model of W. Tonkoff; 
made by Ziegler.) 
Fic. 244. — View of the base of the same model. 
243-244. — 1, Squamosum. 2, Parietale. 3, Capsula auditiva. 4, Cap- 
sula auditiva (cochlear part). 5, Fissura metotica. 6, Epibranchial cartilage. 
7, Sphenolateral plate. 8, Foramen proédticum. 9, Columella. 10, Otie pro- 
cess of quadratum. 11, Basitemporal (postero-lateral part of the parasphenoid). 
12, Articular end of Meckel’s cartilage. 13,Angulare. 14, Supra-angulare. 15, 
Dentale. 16,Skeleton of tongue. 17,Pterygoid. 18, Palatine. 19, Rostrum 
of parasphenoid. 20, Quadrato-jugal. 21, Jugal (zygomaticum). 22, Vomer. 
23, Maxilla. 24, Premaxilla. 25, Anterior turbinal. 26, Posterior turbinal. 
27, Nasale. 28, Prefrontal (lachrymale). 29, Antorbital plate. 30, Interor- 
bitalforamen. 31, Interorbital septum. 32,Frontale. 33,Tectum synoticum. 
34, Foramen magnum. 35, Prenasal cartilage. 36, Orbital process of quad- 
rate. 37, Articular process of Quadrate. 38, Fenestra basicranialis posterior. 
39, Chorda. IX, Foramen glossopharyngei. X, Foramen vagi. XII, Fora- 
mina hypoglossei. 
Fic. 245. — Visceral skeleton of the same model. 
1, Dentale. 2, Operculare. 3, Angulare. 4, Supra-angulare. 5, Meckel’s 
cartilage. 6, Entoglossum — (cerato-hyal). 7, Copula (1). 8, Pharyngo- 
branchial (1). 9, Epibranchial. 10, Copula (2). 
