226 DESCRIPTION OF A SPECDIEN 



The longest diameter is 5 inches. The external and inferior surface has five convolutions 

 converging upward ; the anterior and posterior of these are the continuations of a longitu- 

 dinal rough ridge about 3-4 of an inch broad, which divides this surface from the upper one, 

 which is smooth and rolled into the cavity of the bone. The anterior external convolution 

 runs upward and backward to the point of union with the anterior portion of the petrous 

 bone. The second and third, though at first separated by a deep fissure, become somewhat 

 fused together ; the former is continued into the malleus ; the latter into a bold prominence 

 forming the anterior boundary of an opening, which, on the authority of other writers, I 

 consider the meatus externus. The fourth convolution bounds this notch behind, and the 

 fifth terminates on the posterior end of the bone, a little below the point at which the pos- 

 terior portion joins it. 



The anterior and posterior portions unite with the bulla at their respective ends ; the laby- 

 rinthic. situated at the junction of the two former, is united with the tj'mpanic by the 

 chain of ossicles, which may be appropriately considered now. 



Tlie Malleus. — The absence of the membrana tympani at the time of the examination 

 is much to be regretted, as it causes the loss not only of any observations on its position? 

 but also of any on the homologies of the malleus. This bone is coossified with the bulla by 

 a process presenting a deep groove antei'iorly, which I am inclined to consider the proces- 

 sus longus. The remainder of the bone consists of two prominences tolerably well sepa- 

 rated by a groove ; tlje posterior and larger one is the head ; it presents two articular sur- 

 faces, which meet at an acute angle ; the larger one of these is about vertical, looking back- 

 ward and inward ; the smaller is convex and its general position is horizontal. The anterior 

 prominence represents the manubrium ; a small tubercle on its outer side closes the groove 

 dividing it from the head, and may be considered the homologue of the processus brevis. 

 On its inner side is a horizontal ridge, possibly for the insertion of the tensor tympani. 

 Near its base the manubrium is pierced by a minute canal. 



The Incus has the general outline of a cone with a bent apex. The bone projects back- 

 ward and inward. The base is formed by two unequal articular fixcets, which fit perfectly 

 with those of the hammer. The short process is a mere tubercle on the posterior aspect. 

 The long process is bent upward, and ends in a small oval articulating surface for the 

 stapes, separated from the upper side of the bone by a well marked groove. 



The Stapes is placed rather obliquely, the long diameter of the plate running forward 

 and inward ; it presents for description a head, two crura and a base. The head has no defi- 

 nite boundaries ; there is an oval articular surface on its extremity surrounded by a 

 groove. On the anterior aspect, just before the origin of the crus, there is a rough eleva- 

 tion for the insertion of the stapedius. The posterior crus is the larger and the straighter ; 

 the anterior being slightly curved inward. The base is oval to fill the fenestra ovalis, and 

 is broadest near the anterior end. On the outer aspect the crura diverge so as to leave the 

 entrance to a comparatively large passage between them, which is, however, nearly closed 

 by a plate of bone on the inner aspect. 



The Petrous Portion. — The posterior division is 12 inches long, constricted at its 

 origin, but broad and expanded towards its extremity. It lies in a groove between 

 the squamosal and the exoccipital. Its inferior surface is the only one which presents any 

 points for description. Towards its anterior end it is marked by a deep groove, which at 

 one point is almost made into a canal by a plate projecting from its inner side, and which 



