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 trabeculaB already described. The median 

 plate formed by fusion of the trabeculae 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.) 

 FIG. 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 prooticum. 9, Columella. 10, Otic pro- 

 cess of quadratum. 1 1 , 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- 

 bital foramen. 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. 



FIG. 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) 



