140 COUES ON THE OSTEOLOGY 



have been divided along the median line into a right and left ; but beyond this the palatal 

 fissure is not cleft, but a single broad opening leads into the nares. The anterior single, 

 and posterior double fissures are, however, continuous with each other, as the superior max- 

 illary does not extend far enough inwards to meet the vomer. 



The lateral aspects are each of a subtriangular shape, bounded by the margins of the 

 three surfaces just described, with the planes of which they are united nearly at right an- 

 gles. Their union with the posterior aspect is, however, at less than a right angle, in con- 

 sequence of the lateral tapering of the skull from base to tip. Posteriorly the mastoid 

 and zygomatic processes form conspicuous projections, below and internal to which are 

 the internal organs of hearing. Anterior to this, extending between the under surface of 

 the zygoma and the inferior maxillary articulation, is the pedicellatum, sending upward 

 and forward into the orbit its orbital process. Just above the root of this process is the 

 large circular foramen leading into the cranium, which transmits the second and third 

 divisions of the fifth nerve ; and the pterygoid bones are seen starting from just inter- 

 nal to the root of the orbital process, and running inward to the palatal. 



The orbits occupy by far the largest portion of this lateral aspect of the skull. As usual 

 among the Natatores they are exceedingly defective, not only as to bony margins, but as 

 to septa between the two, and between them and the nasal and pharyngeal passages. The 

 roof is formed centrally by the slight expansion of the frontal bone ; the strongly de- 

 veloped post-orbital processes make a more complete arch posteriorly ; while anteriorly, 

 the slightly developed ante-orbital processes are eked out by the large strong lachrymal 

 bones, which project downwards and backwards from the frontal quite to the malar, and 

 complete the margin anteriorly. A very imperfect floor for the orbits is afforded by the 

 slender elongated malar, the superior border of the inferior maxillary just within the 

 malar, and by the horizontal expansions of the palatal. But the orbit is most defective 

 posteriorly, where a bony parietis is quite wanting, and its place supplied by the temporal, 

 masseter, and pterygoid muscles. The septum between the two orbits is formed by the 

 vertical lamina of the sphenoid and ethmoid, but is very defective, a large circular aj)erture, 

 more than half an inch in diameter, being closed only by dense membrane. Just at the 

 posterior edge of this septum are seen the very large foramina for the optic nerves. 

 There is really only one foramen leading into the cranium ; but this is divided into two by 

 the posterior edge of the vertical sphenoidal lamina, so that the nerves enter the two 

 orbits by separate orifices. Other foramina, for the transmission of nerves and vessels, are 

 found immediately about the optic. On the roof of the orbit is seen the longitudinal 

 groove, emerging from the bony canal which transmits the olfactory nerve ; and anterior 

 and external to it, the large oval aperture which gives passage to the duct of the nasal 

 gland. There is no bony septum between the orbits and the nasal passages. 



Just anterior to the orbits, and separated from them by the lachrymal bone, is a trian- 

 gular space. It opens into the orbits and the nasal passage, and communicates directly 

 with its fellow, and projecting up in it is seen the horizontal incurved lamella of the 

 superior maxillary. It is bounded below by the fused malar and superior maxillary 

 bones, posteriorly by the lachrymal, anteriorly by the descending process of the nasal. 

 This separates it from a large suboval aperture between the mesial and lateral rami of the 

 intermaxillary, which forms the osseous margin of the external nostrils. It is one and a 

 fourth inches long, by one fourth broad. Its axis is parallel with the nasal process of the 

 intermaxillary, and therefore somewhat oblique to the longitudinal axis of the whole skull. 



