188 Charles Searing Mead. 



the long rod-like Meckelian cartilage. Malleus and Meckel's car- 

 tilage form, therefore, at this stage, one continuous piece of cartilage. 

 On the posterior part or malleus proper, one can distinguish several 

 processes, the most prominent of which is the manubrium mallei 

 (Pis. Ill and IV, 7nan. malleus), a long slender process, which 

 curves downward and forward along the inner surface of the future 

 tympanum. Where the forward curvature begins is a slight ventral 

 enlargement, the external part of which forms the processus lateralis, 

 while to the inner part is attached the musculus tensor tympani. 

 Later this inner part forms a prominent process, the processus 

 muscularis. The head of the malleus bears two other prominent 

 processes, one of which extends dorsalward and the other backward. 

 They are both short and rounded and form the two prominences of 

 the saddle-shaped articular surface, by which the malleus articulates 

 with the incus. There is as yet no indication of the processus an- 

 terior (Folii). This arises later in ontogeny as a membrane bone 

 and then fuses with the malleus. 



The size of the cartilages, which later form the ear-bones, is note- 

 worthy. The length of the embryo (head-rump measurement), from 

 which the reconstruction was made, was 30 mm. and that of the 

 head 12 mm. and yet some of the parts of the ear-bones had reached 

 1/4 to 2/5 the size of these elements in the adult. The length of the 

 incus from the upper part of the head to the end of the processus 

 longus w^as 11/25 that of the adult, while the head of the malleus 

 was 1/3 the adult size. At birth the ear-bones have reached prac- 

 tically their full size. This early attainment of their full size would 

 indicate that they are derived from elements which reached a con- 

 siderably larger size in their adult ancestors. This furnishes another 

 point strengthening the hypothesis that the incus is the homolog of 

 the quadrate and the malleus of the articular. 



Nerve Eokamina in the Region of the Ear-Capsules. 



On the median side of the otic capsule, just in front of the point 

 where the pars cochlearis and pars vestibularis unite, is a large 

 shallow pit, the meatus acusticus internum. It is perforated by two 

 openings, the posterior of which is several times as large as the other 



