450 Mabel Bishop 



head is necessary. The double head is broader and flatter, and the 

 snouts are shorter, so that it has a ver}^ blunt, almost square appearance 

 in dorsal aspect. Either component measures 10 cm. from tip of snout 

 to the inion; the head of the normal pig studied measures 14.5 cm. 

 This additional length in the normal specimen is due largely to the 

 rotundity in the frontal, parietal, and occipital regions, a quality totally 

 lacking in the dicephalus. The zygomata of Teras XII are spread later- 

 ally, which, in addition to the flatness of the roof of the slmll, gives the 

 head a much broader aspect through this region, although by actual 

 measurement the distance between the dorsal margins of the outer eye- 

 orbits is less in the Teras than in the normal animal, the former measur- 

 ing 33 nun., the latter 45 mm. Owing to this narrowness between the 

 orbits and the spreading of the zygomata, the outer eyes of XII have a 

 very dorsal position. 



The mandibles on the inner sides of the two snouts are only half as 

 long as the outer ones from symphysis menti to rami. Each of these 

 inner mandibles, instead of articulating with the temporal bone of its 

 respective component, turns its ramus at a sharp angle to the median 

 axis of the body, and the coronoid and condyloid processes of one mandi- 

 ble interlock with those of the other so that an S-shaped appearance is 

 given to the margins of the bones, and a narrow S-shaped interstice 

 is left between them, for they are not united at this point, but merely 

 overlap. On their inferior borders, however, at the angle of the jaws, 

 they are united by a short symphysis. Lying superficial to, i. e., ventral 

 to the symphysis a mass of glandular tissue was removed. From its 

 position it was undoubtedly a median parotid gland. The S-shaped pass- 

 age just referred to lies posterior to the symphysis. The crowding 

 toward the median line of the monster has forced the interlocked rami 

 to turn outward, that is, anteriorly in the direction of least resistance, 

 thus forming a noticeable median protuberance [Plate I, Fig. 2, f]. 

 The maxillary bones of the inner lateral sides of the two components 

 are spread dorso-laterally, that of A somewhat more than that of B. 

 Between them at their posterior margins a small bone has developed 

 which forms a shelf over the protruding rami. Posterior to this region 

 the bones of the roof of the skull are closely knit. The median eye- 

 socket and the adjoining brain cavity lie in the median axis of the mon- 

 ster and largely between the outer eye orbits. 



I have already called attention to the fact that the common carotid 

 takes the name external carotid immediately after giving off the internal 



