SKULL OF ICHTHYORNIS. 125 



A specimen of Ichtlujomis victor (number 1735) had much stouter and 

 deeper lower jaws than I. clispar, but they appear to have contained the 

 same number of teeth. 



In the lower teeth of Ichtlujomis, the pulp-cavity passes well up into 

 the base of the crown. The fang is compressed, and directed downward 

 and forward. It is firmly set in a deep socket, which it nearly or quite 

 fills. The dental succession took place vertically, as in Crocodiles and 

 Dinosaurs ; not laterally, as in Hesperomis, and the Mosasaurs, a fact of no 

 little significance. The young teeth are much inclined when they first 

 appear above the jaw, after the old teeth have been expelled. 



The following measurements of portions of the skull and jaws of 

 Ichthyornis are .from the specimens above described : 



Measurements of Skull. (No. 1459.) 



Transverse diameter of occipital condyle, 3. mm 



Median vertical diameter of occipital condyle, , 2.2 



Distance between upper margins of orbits, 4.5 



Measurements of Jaws. (No. 1450.) 



Extent of tbree sockets for maxillary teeth, 5. mra 



Length of entire lower jaw, 67. 



Extent of alveolar margin, 41. 



Transverse diameter of ramus, 2. 



Greatest vertical diameter, ' 8. 



Transverse diameter of jaw at articulation, 5.5 



Height of crown of tenth tooth, above jaw, . ..-- 2.1 



Depth of ramus, below first tooth, 4.5 



Depth of ramus, below last tooth, 3. 



Measurements of Lower Jaw. (No. 1749.) 



Extent of ramus containing twenty -two teeth, 36.5 mm 



Depth of ramus, below second tooth, 2. 



Depth of ramus, below last tooth, 4.5 



3feasurements of Lower Jaw. (No. 1735.) 



Extent of ramus containing the last eleven teeth, 20. mm 



Depth of ramus, below first of above teeth, 4. 



Depth of ramus, below last tooth, 4.5 



