Royal Physical Society. 383 



It has a slight process on each side, from which springs a short 

 ligament by which the scapula is attached. The par-occipital 

 bone enters considerably into the formation of the base of the 

 skull, and presents three foramina for branchial nerves. It 

 articulates with the basi- occipital, ex-occipital, mastoid, and 

 ali-sphenoid bones. On its cranial aspect, close upon the basi • 

 occipital bone, lies a flat and almost circular otolith, like the 

 one in Silurus glanis (Weber). The basi- sphenoid bone ar- 

 ticulates by a scaly piece with the basi-occipital, and in front 

 of this widens somewhat, and articulates with the ali-sphenoids, 

 it then becomes narrow and elongated, and enters into the for- 

 mation of the nasal part of the skull, and is connected with 

 the orbito-sphenoids, one on each side, and in front of them 

 with the inter-orbital plate, whose flat under surface rests upon 

 it, and anteriorly with the vomer. The ali-sphenoid bone ar- 

 ticulates with the par-occipital, mastoid, post-frontal, orbito- 

 sphenoid, and basi-sphenoid bones, and presents a large notch 

 anteriorly, which is completed by the post-frontal and orbito- 

 sphenoid into a large foramen for the exit of the third, fourth, 

 fifth, and sixth nerves. The or 'bito- sphenoid bone presents on 

 its under surface posteriorly a foramen for the optic nerve ; 

 and the spiculum of bone which separates this from the above- 

 mentioned larger foramen behind it is prolonged into a 

 stiletto-like process, projecting laterally, and passing between 

 the optic and fifth nerves. In front of the orbito-sphenoid 

 bones is the completely ossified inter -orbital plate, broad and 

 squamous in form, and resting on the basi-sphenoid bone, beyond 

 which it projects as a horizontal lamina on each side, and aids 

 the partition of the orbital from the oral cavity. From its 

 upper surface two laminae ascend to articulate with the great 

 frontal bone, and with it complete a segment of the skull. It 

 articulates in front with the pre- frontal bones. The prefron- 

 tals are fused into one, and form a complete tube, continuous 

 with the segment just mentioned, but divided into two by a ver- 

 tical mesial septum, and closed in front so as to leave only two 

 foramina for the exit of the olfactory nerves. The upper surface 

 has a double groove for the nasal bone, and is notched pos- 

 teriorly where it enters into the anterior wall of the opening. 

 At the anterior lateral angle is a smooth surface for articula- 

 vol. i. 2 L 



