566 GEOLOGICAL SURVEY OF THE TERKITOEIES. 



princippJ extent posterior to the zygomatic arch, and is in form like a 

 trough, the inferior edge being recurved from the squamosal i^rocessto 

 the summit of the occipital crest. It is narrow within the zygomatic 

 arch, which is short, inclosing a space whose length is less than one- 

 fourth that of the cranium. 



The occipital bone extends but a short distance on each side of the 

 condyles, and is separated from the mastoid by an irregular- suture, 

 which is pierced by a large mastoid foramen. On the inferior face, near 

 to each condyle, and one-third the distance from its inner extremity, is a 

 posterior condyloid foramen, isolated by a narrow bar from the extremity 

 of the foramen lacerum posterius. The paramastoid process is repre- 

 sented b^' a small tuberosity, and the mastoid by a rather larger one, 

 some distance anterior to it. 



The meatus auditorius opens upwards just below the external ridge of 

 the temporal fossa, and at a little distance behind the post-glenoid pro- 

 cess. Its canal contracts rapidly, and extends upwards and backwards 

 towards the labyrinth. It is separated from the forame7i lacerum by but 

 a thin wall, and if there was an expansion of the caviim tympanic it must 

 have been exceedingly small, owing to the close approximation of the 

 mastoid to the basi-occipital and sphenoid at this point. The labyrinth 

 is lodged in a petrous mass opposite the occipito-mastoid suture, and the 

 canals are small. 



The hasi-occipital contracts anteriorly, and with the sphenoid forms an 

 uninterrupted boundary of the foratnen lacerum. This terminates oppo- 

 site to the posterior boundary of the external meatus, and gives rise to a 

 wide, shallow groove, which extends anteriorly between the pterygoid 

 ala and the post-glenoid process, and turning outwards round the latter, 

 grooves it. Opposite to the post-glenoid process, and just posterior to the 

 end of the pterygoid, a small foramen enters, which is probably the fora- 

 men ovale. Almost continuous with it is a canal which pierces the base 

 of the pterygoid lougitudinallj", and issues in an excavation of its exter- 

 nal face near the sphenoid. 



The pterygoids are remarkable for their great length, inclosing, as they 

 do, with the palatine process, a deep, narrow, trench-like fossa, which 

 measures almost the entire length of the zygomatic fossa. Processes of 

 the sphenoid contribute to these walls, (which are thus double.) and the 

 sphenoid roof is strongly concave. The alisplienoid is elongate antero- 

 posteriorly, and is principally in contact superiorly with the frontal ; an- 

 teriorly it has a short suture with the lachrymal. Almost its entire length 

 is traversed by a shallow groove which terminates in a small foramen 

 opticum, opposite to a point marking the posterior third of the zygomatic 

 fossa. The foramen rottindttm issues as usual between the alisphenoid 

 and the pterygoid, but is considerably anterior as well as inferior to the 

 f. opticum. I cannot determine whether the orbitosphenoid is distinct. 



The lachrymal is a large bone, of a triangular outline, the shorter 

 side being inferior. It is entirely on the inner face of the orbit, and, 

 as in the elephant, sepai-ates the frontal and maxillary by its superior 

 lirolongatiou. Its inferior border is slightly notched in front by the 

 large /om /new infraorhitale posterius, and the anterior is deeply emar- 

 giuate, passing behind the small /. lachrymale. 



Tlie palate is remarkable for its length and narrowness. Its roof is 

 chiefly composed of the niaxillaries, but a very short portion is formed by 

 the palatine plates of the o. o. palatina. These are i^roduced into a 

 median point behind, between the nares, and exteriorly form the inuer 

 wall of the postnareal trough for a considerable distance. The closeiy 

 united maxillaries form the outer wall for a short distance, being pro- 



