316 MR. W. H. FLOWER OX THE OSTEOLOGY OF THE SPERM-WHALE. 



Li the section of the large skull, the suture between the basisphenoid and presphe- 

 noid, and also that between the ethmoid and the frontal, are distinct ; all the others are 

 obliterated ; but they can be traced more or less distinctly in the young skull. 



The portions of the wall formed by the basioccipital below, and by the frontal above, 

 are very thin, while those formed by the occipital above, and the conjoined presphe- 

 noid and ethmoid in front, are of vast thickness. The portion of the frontal divided in 

 the section belongs to the bone of the right side, which extends somewhat over the 

 middle line. As in the dolphins generally, the parietal forms no part of the boundary 

 of the brain-cavity in the middle line, but is seen to form part of the lateral wall of 

 the cavity, resting on the alisphenoid, and having the frontal in front and the occipital 

 behind. Above, it has so completely coalesced with the occipital, that even in the young 

 skull its limits cannot be distinguished. The bones forming the periotic capsule are 

 completely excluded from the brain-cavity, and in the adult skull removed to a distance 

 of 14" from it. By the aid of the mobility of the squamosal in the young specimen, a 

 minute portion of this bone, ^" by J" in dimensions, can be traced in the lateral wall of 

 the interior of the cranium, between the alisphenoid and the parietal. 



The foramina at the base of the cranium are only five in number. Several of the 

 nerves find their exit from the cavity by common canals, which divide in passing through 

 the immense mass they have to traverse before reaching their destination. 



1. An oval foramen, ^" in its greatest diameter, situated about 1" from the middle 

 line, at the junction of the frontal and ethmoid*. It leads into a canal (9" long on the 

 left side) which runs forwards and outwards, traversing the last-named bone, and 

 opening into a wide fissure in the posterior part of the narial passage between the 

 ethmoid and the vomer. On the right side, the foramen is smaller, and, owing to the 

 conformation of the bones, the canal runs a much shorter course, opening rather behind 

 the upper margin of the blowhole, between the frontal and the ethmoid. This would 

 probably allow the exit of a small olfactory nerve, distributed in the simplest possible 

 manner on the mucous membrane of the air-passage. In several dolphins there are 

 similar channels through the ethmoid bone, though unaccompanied by any increase of 

 extent of olfactory surface by turbinal bones as in the Whalebone-Whales. 



2. The exit of the optic nerve is by a comparatively small foramen in the anterior 

 wall of the skull, transversely oval, 1" by -6", 2" from the middle Hue, 3" below the last- 

 mentioned foramen, and about the same distance above the junction of the presphenoid 

 with the basisphenoid. The course of the long canal to which this leads, is outwards, 

 and slightly forwards. The distance from the wall of the brain-cavity to the upper 

 margin of the orbit, is nearly 4 feet. 



3. A large oval foramen, situated between the orbitosphenoid plate of the presphe- 

 noid and the alisphenoid, 2" in greatest diameter, and leading into a canal which passes 



* In the cist taken from the interior of the cranial cavity, figured at p. 372, this small foramen has yielded 

 no impression. The relative size and position of the four others are well seen. 



