OF THE MAMMALIAN OSSICULA AUDITUS. 415 



to the malleus in quite young skulls, has a well-developed body and stout crura, the 

 posterior diverging as much as the processus longus. The crura of the stapes are very 

 straight, rather short, and very divergent ; the posterior is inserted into the base at a 

 marked distance from its extremity. There does not ever appear to be any bony canal 

 between the crura, either in Hystrix or Cercolabes. The base is very broad vertically as 

 well as horizontally, and rather convex towards the vestibule. 



In Hystrix javmiica the angular projection on the inner border of the manubrium 

 mallei is even better-marked than in H. cristdta. In the Guiana Tree-Porcupine (Cerco- 

 labes insidiosus, PI. LX. fig. 25) the manubrium is like that of Hystrix ; but the head is 

 more massive than in the common Porcupine's, and still more than in the elongated 

 mallei of Cavia, Chinchilla, &c. The stapes has a rather narrow but very stout base, 

 convex towards the vestibule ; and the crura, as in Mus and Hydrochcerus, are not widely 

 divergent. There is no bony intercrural canal. 



Among those Eodents arranged by Mr. Alston (I. c.) under the family Octodontid^;, 

 in the Ground-Pat (Aulacodus swindemianus, PL LX. fig. 27) the head of the malleus is 

 still more produced forwards than in Hystrix, and there is as little trace of a lamina ; but 

 in the manubrium it differs from the Porcupine's in having no projection on the inner 

 border, the processus muscularis being a prominent tubercle close to the root of that border. 

 The outer aspect ends in a very broad spatulate dilatation. The fusion of the malleus and 

 incus is complete ; the line of junction is very faint. The processus brevis of the incus 

 does not diverge so much as in Hystrix. The crura of the stapes are slender and very 

 divergent ; both are inserted into the base a distinct distance from each extremity ; and 

 there is no bony intercrural canal in the recent skeleton. The base is very broad 

 vertically and horizontally. 



In Pournier's Oapromys (Capromys pilorides, PL LX. fig. 26) the head of the malleus 

 is as much produced forwards as in Aulacodus ; the manubrium, however, resembles that 

 of Hystrix, as the processus muscularis (p m) is placed on the middle of the inner border*. 

 There is the same obtuseness of the angle corresponding to the processus brevis (p b) as in 

 all these Hystricomorpha. The fusion of the malleus and incus is so complete that the line 

 of demarcation is often quite effaced, especially posteriorly. The stapes is very small in 

 proportion to the other ossicles, as is seen in Basyprocta ; the crura are thick, short, and 

 not widely divergent ; the base is very broad ; and an intercrural bony canal exists in some, 

 but not all, of the skeletons of this rodent in the Museum of the Poyal College of Surgeons. 



Hyrtl states that in the Coypu (Myopotamus) the malleus and incus are not anky- 

 losed ; no ossicula of this animal have yet been prepared for the College collection. 



In a skull of an Octodon cumingii, six weeks old, the author found the malleus and 

 incus quite unankylosed (PL LX. fig. 28). The former ossicle is rather different from 

 the same in the above animals. The upper part of its head is ill-developed, and hardly 

 projects above the articular stu'face ; the latter is narrow and deeply cut; the neck is 

 very short ; the manubrium is long, and not so broad at the base as in the Porcupines 

 and Pats ; it bears a trace of a processus brevis (p b) ; and the processus muscularis 

 (pm) is halfway down the inner border of the handle. There is, as usual in this 



* The letters^) »i in the lithograph are placed too near the processus longus of the incus. 



3k2 



