THE SKULL 



281 



join together in the middle line. The nasal capsule is separated 

 from the orbit of its side by the lamina orbito-nasalis, which 

 reaches from the trabecula to the orbital cartilage. The roof 

 is often very incomplete, and may be formed only in front and 

 behind. That part of the roof which connects the two 

 auditory capsules is called the tectum synoticum. 



The relations of the trabecular are of importance, for the 

 hypophysial fenestra which they enclose between them also 



PQ, 



Fig. 129. — Diagram of a schematic chondrocranium seen from the left side, 

 and showing the relations of the cartilages to the principal nerves and 

 blood-vessels. 



This diagram does not represent any particular form, but shows the type 

 on which nearly all skulls are built, abn, abducens nerve ; ac, auditory 

 capsule ; at, ala temporalis ; btp, basal process ; hf, hyomandibular facial 

 nerve ; ic, internal carotid artery ; jv, jugular vein ; Ion, lamina orbito- 

 nasalis ; 0, occipital arch ; oa, orbital artery ; oc, olfactory capsule ; ocn, 

 oculomotor nerve ; oln, olfactory nerve ; on, optic nerve ; op, otic process ; 

 pa, ascending process ; pf, palatine facial nerve ; pp, pila antotica ; pq, 

 ptery go-quadrate ; pv, pituitary vein ; rop, profundus ophthalmicus nerve ; 

 tc, trabecula ; vn, vagus nerve. 



serves for the admission of the internal carotid arteries to the 

 brain-case. In those cases where the trabecular are wide 

 apart from one another, as in the frog, the skull is said to be 

 platytrabic (or platybasic) ; in others, such as the trout, the 

 trabecular are close to one another and fuse in the middle line, 

 and this condition is called tropitrabic (or tropibasic). 



The splanchnocranium consists of the pterygo- quadrate 

 of the upper jaw, Meckel's cartilage of the lower jaw, the 



