1906.] Allen, Mammals from Western Mexico 201 



mm.! In the females the range, with one exception, is from 61.5 

 to 69 mm., with various intermediate stages in both series, as shown 

 in the subjoined table of measurements. 



There is, further, a striking variation in the structure of the 

 middle region of the ventral aspect of the skull. This consists in 

 the presence or absence of an elongated bulbous expansion outside 

 of the walls of the narial passage. This expansion is due apparently 

 to the development of a large sinus between the two plates of the 

 orbitosphenoid. It is convex externally, with a transverse diameter 

 of 10 to 15 mm., a vertical diameter of 15 to 20 mm., and a length 

 of 35 to 40 mm., or more, it extending posteriorly to or slightly 

 beyond the plane of the palatal notch, and anteriorly about to a 

 plane passing between m 1 and m 2 . Its external wall is thin, papery, 

 and generally very fragile ; the enclosed cavity may be entirely hollow 

 or more or less filled with inosculating bony lamellae. This bulbous 

 expansion of the orbitosphenoid is present in rather more than half 

 of the Escuinapa series of skulls (in 12 out of 21), and also in about 

 the same proportion in the Peccary skulls from other Mexican and 

 United States localities; it is developed symmetrically in both orbito- 

 sphenoids, but varies more or less in size, according to the extent to 

 which it may be developed in different specimens. It is also present 

 in both sexes, and in young specimens which still retain the entire 

 milk dentition as well as in adults. 



Associated with this striking modification of the orbitosphenoids 

 is an abnormal inflation of the maxillary arm of the zygoma and 

 of the lower part of the lachrymal which become often enormously 

 expanded, with thick walls enclosing a sinus, contributing still further 

 to greatly modify this portion of the skull. (See Plate XX, and ac- 

 companying descriptive matter.) It is evident that this strange 

 modification of tha orbitosphenoids and adjacent parts is patho- 

 logical in character, due probably to the presence of parasites, that 

 can readily find their way from the sinuses of the posterior nares into 

 the maxilla and adjoining parts of the skull. 



In this connection an examination has been made of nearly 50 

 skulls of Peccaries in the Museum collection from various parts of 

 South America, with the following results: In a series of 17 skulls of 

 T. pccari from the Santa Marta district of Colombia, all were found 

 diseased in the manner above described, so that this condition might 

 readily be mistaken for the normal. In 20 skulls of T. iorvum about 

 80 per cent, show the diseased condition strongly, and others show 

 traces. Of 9 skulls of T. tajacu from Chapada, Matto Grosso, Brazil, 



