62 



246. A skull of the same species, vertically bisected. 



Presented by Fr. Bennett, Esq., F.L.S. 



247. Three caudal vertebrae of the Tunny (Scomber Tfiynnus, Linn.; TJtynnus vul- 

 garis, Cuv.). 



The bodies are flattened laterally, the neural and hsemal arches depressed and extended 

 horizontally backwards so as to give a four-sided shape to the vertebrae. The flattened 

 neural and heemal spines of one vertebra are pressed, as it were, into the neural and heemal 

 canals of the succeeding vertebra, so as to retain their connection, the series being naturally 

 articulated or interlocked. A line of division may be seen at each articular extremity, be- 

 tween the terminal osseous cones and the intervening part of the centrum ; but a vertical 

 section through the middle of the centrum shows that they have completely coalesced at that 

 part, and also exposes a vascular cavity continued from the haemal canal upwards. 



Hunterian. 



248. The skull of a large Sword-fish (Xiphias gladius). 



The mesotympanic has coalesced with the epitympanic, but the pretympanic and hypo- 

 tympanic continue distinct. The stylohyal articulates with the upper extremity of the coa- 

 lesced mesotympanic. The wide and shallow form of the basicranial canal is well shown 

 in this specimen. 



Mus. Brit. 



249. The prolonged premaxillary rostrum, or sword, of a Xiphias, with the pre- 



frontal and part of the frontal bones. Hunterian. 



250. A vertically bisected incomplete skull of a Sword-fish (Tetrapturus belone), 



with the first two vertebrae. 



The alveolar borders of the upper and lower jaws are beset with minute villiform teeth, and 

 the like extend along the sides and under part of the rostrum or ' sword,' which is formed 

 chiefly by a prolongation of the premaxillaries, and is rounded in the present genus. In both 

 genera of Sword-fishes the whole of the anterior part of the extensive interorbital space is 

 occupied by the prefrontals, which join each other at the median line by an extensive verti- 

 cal cellular surface : they form the anterior border of the orbit, and the posterior wall of the 

 nasal fossa ; they close the cranial cavity anteriorly, and transmit the olfactory nerve to the 

 capsule by a central foramen. They are almost entirely covered by the frontals above, which 

 they support by a broad flat surface ; a very small portion only appearing on the upper sur- 

 face of the skull at the anterior angle of the orbital ridge. Were the frontals separated, the 

 prefrontals would then appear, as hi the frog, at the median line : were the suture between 

 the two prefrontals to be obliterated in Xiphiat, an ' os en ceinture ' would be produced like 

 that of the frog. The nasal bone of the Sword-fish, which Cuvier calls ' ethmoide,' presents 

 a cellular structure of its base, designed to break the force of the concussion arising from the 



