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Family Myopotamidee. 



Genus Myopotamus. 

 Dental formula : t 1=|, p j=|, m ^=20. 



2039. The skeleton of the Coypu (Myopotamus Corpus). 



The vertebral formula is : 7 cervical, 13 dorsal, 6 lumbar, 4 sacral, and 21 caudal. The 

 transverse processes of the last cervical, being represented only by the diapophyses, are im- 

 perforate ; those of the first dorsal are shorter, but much thicker, and are excavated at the 

 extremity for the reception of the strong tubercle of the very short first thoracic rib. The 

 spine of the second dorsal is remarkable for its sudden and extreme elevation ; that of the 

 last dorsal being almost rudimental, like those of the last five cervicals : the spine of the 

 dentata is produced backwards above the posterior cervical vertebrae. The spine of the 

 twelfth dorsal is that to which those of the other trunk-vertebrae converge. The diapophy- 

 sis of the sixth dorsal vertebra supports a tubercle which in the succeeding vertebrae expands, 

 and then divides at the twelfth dorsal into the anapophysis and metapophysis. The former 

 subsides in the last lumbar, but the latter is continued along the sacral and a great part of 

 the caudal region, continuing after the true zygapophyses have disappeared. Eight pair of 

 ribs articulate directly with the sternum, which consists of six bones. The clavicles are com- 

 plete. The acromion is of unusual length and slenderness, exceeding the extent of its base, or 

 spine of the scapula ; it is expanded and sub-bifid at its extremity. The border of the supra- 

 spinal fossa rises into an obtuse angle, but the infraspinal fossa surpasses it in breadth. The 

 humerus is pierced between the condyles, but not above the inner condyle : the deltoid process 

 is long and well defined. The femur has no third trochanter. A fabella is preserved behind 

 each external condyle. The bones of the right leg of this skeleton have been fractured and 

 united. The bones of the hind foot are long and well developed ; and the breadth of this 

 member, which is webbed, together with the long and strong tail, give the species great power 

 of swimming. The scalpriform incisors are proportionally of unusual size. The temporal 

 fossae meet at a low ridge upon the parietal. The paroccipitals are relatively as strongly 

 developed as in the Capybara ; and the true mastoids also extend downwards in the form of 

 three-sided, pointed processes, nearly half the length of the paroccipitals. In the general 

 character of the lower jaw, the Coypu resembles the Capybara. The antorbital vacuities 

 are very large, but the lacrymals are extremely reduced in size, and are grooved by the 

 lacrymal duct. 



Presented by Sir Everard Home, Bart., V.P.H.S. 



2040. The lower jaw of the Coypu (Myopotamus Coypus). 



It shows the deciduous molar and the first and second true molars ; the third molar is just 

 appearing. The outer walls of the sockets have been removed in the left ramus, showing the 

 division of the base of the milk molar and first true molar into fangs. The germ of the 



3B 



