CHAP, in.] SKELETON OF THE HEAD AND TRUNK. 85 



maxilla is the lasi-fadal axis (If), and the two axes in the cat form 

 an angle of 145. 



The basi- cranial axis forms with the foramen magnum (fm) an 

 angle of 110, while with the cribriform plate (cp) it forms one of 

 155 open upwards and backwards. 



The extreme length of the line (c), slightly exceeds that of the 

 basi-cranial axis (be), while it is itself somewhat exceeded by the 

 cerebral length, i.e., the length between the front end of the olfactory 

 fossa and the hind-most point of attachment of the tentorium. 



As to the details of the parts shown in a median vertical section, 

 we see in the first place the large cerebral chamber (Fig. 49, s, t), in 

 front of which is the more solid, facial part with the mesethmoid (me) 

 interposed between the vomer (v) below and the inflected plates of 

 the frontal and the nasal (/, n). 



The cerebral chamber is seen to be bounded behind by the bony 

 tentorium descending as a free process from the hinder end of the 

 parietal (p), and being attached to the inner anterior margin of the 

 petrosal. In the petrosal we see the internal auditory opening (ai) 

 in a fossa, from the anterior part of which (af) proceeds the aqueduct 

 of Fallopius. Above and slightly behind this fossa, is seen that for 

 the cerebellar process. We see also the concavity of the pituitary 

 fossa in the upper surface of the basi-sphenoid (sg), with the large 

 air- cavity in the pre-sphenoid (ps). In the ex-occipital we see the 

 anterior condyloid foramen (for transmitting the hypoglossal nerve), 

 with another foramen, for a vein, behind it. 



"When the skull is cut vertically a little on one side of the antero- 

 posterior median line we then see (Fig. 50) the frontal sinus (fs) 

 extending backwards over the anterior part of the cranial cavity. 

 We also see how the ethmo-turbinal, or lateral ethmoid, sends its 

 lamella quite upwards in front of the frontal sinus (the upper et), 

 as well as horizontally forwards (the lower et of Fig. 50). We also 

 see more plainly (than in the perfectly median vertical section) 

 the contrast which exists between the direction followed by the folds 

 and furrows of the ethmo-turbinal and that which the folds and 

 furrows of the maxillo-turbinal (mf) follow. 



When the skull is divided vertically through the external auditory 

 meati (i.e., transversely, or in the direction of the coronal suture) we 

 see that the basilar part of the occipital forms as it were a centre. 



The anterior part of such a section shows the great cranial arch 

 rising above this centre and closed in front, while below it, is the 

 arch of the lower jaw and farther forward the arch of the upper 

 jaw enclosing- the double tube of the nostrils, which extends from 

 the anterior to the posterior nares. 



The posterior part of the section shows us the hinder part of the 

 great cranial arch rising above around the foramen magnum 

 behind, while below it, is the arch of the hyoid extending downwards 

 on each side from the tympano-hyals to the basi-hyal. 



As to the CAVITIES OF THE SKULL : the two orbits are separated 

 one from another in part by the cranial cavity (behind the cribri- 



