1910.] The Skull of Solenodon paradoxu.s. 245 



The orbitosphenoid is of the Placental type, that is it is pierced by the 

 optic foramen and is not depressed dorsoventrally in such a manner that the 

 opposite sphenorbital fissures are confluent below it (contrast Marsupials). 

 In the sagittal section of the skull the anterior portion of the orbitosphenoid 

 is seen to be invaded, as it is in Didclphis (p. 221), by the backward prolon- 

 gation of the ethmoidal chamber. 



The alisphenoids form the lateral wings of the basisphenoid and in the 

 young skull, as also in the embryonic Centetes, are not suturally separate 

 from that bone. The temporal wing of the alisphenoid is relatively much 

 smaller than in Didelphis, and, as in typical Placentals, it is pierced by the 

 alisphenoid canal and is excluded from the glenoid fossa. A descending 

 flange forms the backward continuation of the pterygoidal ridge and an 

 external inferior branch runs outward to meet the postglenoid crest of the 

 squamosal. This branch is not curved posteriorly for the tympanic cham- 

 ber (contrast Cenieies). 



The basisphenoid contrasts with that of Erinaceus, Centetes and Micro- 

 gale in lacking the descending lateral wing, which in those genera embraces 

 the tympanic cavity. On the dorsal or cerebral surface of the basisphenoid 

 (as shown in a sagittal section) the pituitary depression is absent and, as in 

 Marsupials and Erinaceus, there are no anterior and posterior clinoid proc- 

 esses. In Centetes however a small posterior clinoid process is present. 



Between the basi- and pre-sphenoids in the median line, in the young 

 Solenodon (Fig. 18, A), is a small hole which appears to be homologous 

 with a similarly placed foramen in Centetes; in the latter genus this foramen 

 lodges a ventral apophysis of the vestigial chorda dorsalis (Leche, 1907, p. 

 68). Parker (1886, pi. 19, figs. 1-4) figures a similar foramen in Erinaceus 

 but called it a "pituitary hole," although one of his specimens (fig. 3) seems 

 to have retained a considerable piece of the notochord. Mead (1909, figs. 2, 

 5) shows that in the Pig also the vestigial notochord communicates with the 

 pharynx. The ventral surface of the pre- and basisphenoids is flat as in 

 Microgalc, whereas in Centetes, Ericulus and Erinaceus there is a large round 

 pit in the median line surrounding the foramen for the chorda. 



The basioccipital, as in Centetes, Microgale, certain Creodonts and INIar- 

 supials is very short. This bone bears a pair of accessory occipital condyles 

 and the latter together with the exoccipital condyles are much Hke those in 

 Centetes. Paroccipital processes of the exoccipital are lacking in the young 

 skull (contrast other Zalambdodonts) but are indicated as a pair of small 

 knobs in the old female. They are also lacking in the skull of Solenodon 

 cubanus figured by Leche (1907, p. 72). 



The auditory prominence of the petrosal is larger than in Centetes. It is 

 ovoid, with the inner side closely appressed to the basioccipital whereas in 



