OF THE MAMMALIAN OSSICULA AUDITUS. 433 



sideration ; Hyrtl devotes a long and interesting chapter (I. c.) to the vessels of the 

 mammalian tympanum, chiefly dwelling on the stapedial artery and its "branches. 

 According to that anatomist, this vessel seems, in Urinaceus and other Insectivora, to 

 end ultimately in branches distributed to the orbit, whilst the homologue of the internal 

 carotid is given off before the stapedial artery enters the canal between the crura of the 

 stapes; but the distribution of these vessels, and the extent to which they are sur- 

 rounded by bony canals, differ in certain families. Still that is a subject which does 

 not pertain to the distinctions of the auditory ossicles in the same animals. 



The ossicula of the Shrews (Sorex) are best studied in the crania of some of the large 

 American species (PL LXII. figs. 1, 2). 



The malleus is readily detached from the skull by maceration, together with the 

 tympanic bone, which is almost identical in its ring-like undeveloped character to its 

 homologue in the Marsupials. By the aid of a fine needle the ossicle may be separated 

 from the tympanic without fracturing the processus gracilis. 



The head is small, as in most laminated mallei. It bears a rather deeply cut articular 

 surface, with two facets, of which the uppermost is the larger, and the lower the more 

 convex. The neck is long and thin, and midway between the head and manubrium it is 

 bent on itself, forming a sharp angular projection. At the point where it joins the 

 manubrium is attached a prominent globular process of bone (PL LXII. figs. 1, 2, oa), 

 which projects downwards and backwards in the natural position, and seems, as it were, 

 to push aside the handle outwards and forwards. The manubrium itself is as thin and 

 slender as in most Marsupials. A distinct angle, corresponding to the processus brevis, 

 exists ; it may be seen at the base of the manubrium, projecting anteriorly to the 

 globular process. The extremity of the handle is almost styliform, although, with the 

 aid of a strong lens, I have detected not only a slight spatulate dilatation, but also an 

 outer surface to the manubrium, extremely narrow, yet sharply bordered from the very 

 thin and compressed sides *. 



The lamina is as wide as in a typical terrestrial Carnivore, and runs forward with the 

 processus gracilis without receiving a thin process from the front of the head, such as is 

 seen to join the processus gracilis in most laminated mallei. That process is flattened, 

 narrow near the root, but wide in the middle, tapering to a point at the extremity ; it is 

 closely applied to the tympanic bone. 



A very small tubercular elevation on the inner side 6i the neck, close to where it join s 

 the manubrium, represents the processus muscularis. To study the relation between 

 this process and the orbicular projection from the neck, a malleus of a Sorex should be 

 placed side by side with one from a Gymnura, where both exist well developed t (PL 

 LXII. figs. 2 oa & 14). 



The exact morphological signification of the orbicular process is a difficult point to 

 decide. It exists in many Insectivora and in many of the Muridse. It clearly cannot be 



* For a fuller explanation of this expression, " sharply bordered from the sides," see descriptions of the malleus in 

 the terrestrial Carnivora. 



t This elevation can only properly be seen by placing a very clean malleus of Sorex on a piece of black paper, and 

 viewing it under the microscope with a 1-inch object-glass. 



