354 THE ANATOMY OF VERTEBRATED ANIMALS. 



meatus, at the inner end of which is a circular elevation for 

 the attachment of the tympanic membrane. A short distance 

 internal to this frame for the membrane of the drum, a low 

 crest rises from the floor of the bulla and imperfectly divides 

 it into an outer and anterior portion which communicates 

 with the Eustachian tube, and an inner blind spheroidal cavity 

 which occupies the greater part of the bulla. The part of the 

 bulla which forms the floor of this cavity is the result of the 

 ossification of a process of the periotic cartilage, while the 

 other part is furnished by the tympanic bone. The low crest 

 is produced by the conjunction of both. Posteriorly and in- 

 ternally, the periotic region of the bulla presents a canal, 

 through which the internal carotid artery passes. The pos- 

 terior opening of the carotid canal looks into the foramen 

 lacerum posticum^ and is not visible without dissection. 

 There is a large paroccipital process, with a prominent free 

 extremity ; but, for the greater part of its length, it is closely 

 applied to the back of the bulla. The condyloid foramen is 

 quite distinct from the foramen lacerum posterius. A large 

 foramen behind the glenoidal cavity transmits a vein from the 

 interior of the skull. In the nasal cavity, the ethmoidal turbi- 

 nals are very large ; the superior turbinals are prolonged into 

 the great frontal sinus, and the inferior turbinals unite, in the 

 middle line, with the septum. 



The clavicles of the Dog are always rudimentary^, and are 

 generally represented only by a gristly intersection of the 

 muscles which represent the sterno-mastoid and deltoid. 



The olecranar fossa of the humerus is perforated. The 

 hallux is much shorter than the oth«^r digits. When the Dog 

 stands, the metacarpal bones of these digits are nearly verti- 

 cal ; the basal phalanges are horizontal ; the middle and the 

 distal phalanges are inclined in the form of a V with the apex 

 (the articulation between the two) downward. The claws 

 are, consequently, raised from the ground, the foot resting 

 partly on a thick integumentary pad, which lies beneath the 

 basal phalanges; and, partly, on the under surfaces of the 

 joints between the middle and the distal phalanges. The dis- 

 tal phalanges are kept bent upon the middle ones by elastic 

 ligaments, which pass from one to the other, and which an- 

 tagonize the action of the long flexors. The Dog, therefore, 

 possesses the mechanism for the retraction of the claws, but 

 its action is not sufficient to protect them from wear. Fahellce^ 

 or sesamoid bones developed in the tendons of the gastrocne- 

 mius^ lie behind the condyles of the femur. The fibula is thin 



