168 Scientific Proceedings, Royal Dublin Society. 



the nasal bone overlies the nasal sacs. Other facial bones are the 

 maxilla and premaxilla, and, connecting the skull with the shoulder 

 girdle, is a forked post-temporal bone, from the concavity of which 

 three small scales of bone pass to the inner, and one to the outer, 

 ridge of the pterotic bone. Before passing to the hyoid apparatus 

 and gills, a more particular description may be given of the above- 

 mentioned bones. 



The frontal is the largest bone in the skull, and consists of two 

 lateral halves fused. From the back of the upper surface projects 

 an elevated ridge, which is continuous with the crest of the supra- 

 occipital, the latter being wedged into a deep groove behind it. 

 At the sides of this are a pair of ridges, continuous with the inner 

 ridges of the pterotics. These ridges are undermined from the 

 outer side by deep grooves, which lodge mucous glandular tissue 

 in the recent state. They communicate with a pair of curious 

 oval apertures, which lie in front of the central ridge. Laterally 

 the bone projects over the orbit, forming its roof. On the under 

 surface are seen two curved ridges, the anterior ends of which 

 articulate with the prefrontals, and the posterior with the alisphe- 

 noids. Just external to the articulation with the prefrontal is a 

 groove, through which the nasal branch of the trigeminal nerve 

 passes, and external to this the bone again articulates with the 

 prefrontal. Stretching forwards over the latter, the frontal arti- 

 culates with the ethmoid. Posteriorly it articulates with the sphe- 

 notic, parietal, and supraoccipital, and only just touches the inner 

 ridge of the pterotic. The frontal overlaps every bone with which 

 it articulates. 



The supraoccipital consists of a large elevated crest, continuous 

 with the median ridge of the frontal, and of two small lateral 

 portions. These articulate with the epiotics externally, and the 

 articulations are overlapped by the parietals, which also articulate 

 with the supraoccipital farther in front. The under surface of the 

 crest articulates below with the exoccipitals, and Ihe latter, uniting 

 together, exclude the supraoccipital from the foramen magnum ; 

 in front it articulates with the frontal. The back of the crest is 

 closely connected by ligamentous fibres to the neural spine of the 

 atlas. 



The parietal is a curved scale of bone, presenting a well-marked 

 ridge, which runs from before backwards, with an inclination out- 



