120 



Mil. E. PHELPS ALUS, JUN., ON 



posteriorly and joins the ventral end of the postorbital process, 

 this ridge forming the boundary between the horizontal portion 

 of the suborbital shelf and its ventrally projecting eaves-like 

 lateral edge. Between its dorsolateral and ventro-lateral 

 processes the remainder of the antorbital process is a wide and 

 gently rounded surface which extends from the orbit to the 

 nasal capsule, and is so completely fused ventrally with the 

 dorsal edge of the palatoquaclrate that even the line separating 

 the two cartilages cannot be recognised. 



The suborbital shelf is a wide thin plate of cartilage Avhich 

 extends between the antorbital and postorbital processes, and 

 has a narrow, ventrally projecting, eaves-like lateral edge, just 

 above referred to. The shelf is prolonged posteriorly beyond the 

 postorbital process, this postorbital portion of the shelf projecting 

 ventro-posteriorly at a slight angle to the orbital portion, and 

 apparently representing, as just above explained, the processus 

 oticus quadrati. It gives origin, on its ventral surface, to the 

 musculus protractor arcuum branchialium of better's (1878) 

 descriptions. On the ventral surface of the continuous shelf 

 these two portions are separated from each other by a groove 

 which lies directly ventral to the ventral end of the postorbital 

 process and is directed postero-mesially. That part of the 

 orbital portion of the shelf that lies lateral to the foramen for 

 the nervus hyoideo-mandibularis facialis belongs to the palato- 

 quadrate, and is probably formed by the epal (quadrate) and 

 pharyngeal portions of the mandibular branchial bar, the 

 pharyngeal element not projecting as a processus basilaris. 



The cranial cavity has large anterior and posterior portions, 

 separated by a narrow neck in the orbital region, this neck 

 lying between the ventral edge of the azygous portion of the 

 membranous interorbital wall and the summit of the rounded 

 transverse presphenoid bolster. The posterior portion of the 

 cavity is tall, with a concave anterior edge the dorsal end of 

 which projects dorso-anteriorly above the orbit like the horn of 

 a crescent. The postclinoid wall lies at about the middle of the 

 length of this posterior portion of the cavity and projects 

 anteriorly or antero-dorsally. Between it and the foramen 

 magnum there is a depression in the cranial floor, and anterior 

 to it, between it and the presphenoid bolster, is the large 

 pituitary fossa. The postero-dorsal end of the hypophysial 

 groove on the ventral surface of the basis cranii lies slightly 

 posterior to the summit of the presphenoid bolster. A slight 

 transverse ridge at about the posterior quarter of the pituitary 

 fossa marks off a small posterior and deeper portion of the fossa. 

 The foramina for the nervi facialis, trigeminus, and abducens lie 

 dorsal or postero-dorsal to the postclinoid wall, and the small 

 foramen for the pituitary vein antero-ventral to it. 



The anterior portion of the cranial cavity increases gradually 

 in height from its hind end up to the base of the median rostral 



