638 INSECTIVORA. 



the cerebellum, and often leaves the optic lobes uncovered ; 

 its surface is smooth, except for one shallow longitudinal sulcus 

 on each side. The corpus callosum is small and the anterior 

 commissure large. The stomach is simple (except in Galeo- 

 pithecus). A caecum is present or absent. There are two 

 superior venae cavae. 



The testes are inguinal or abdominal and never descend into 

 a scrotum. The penis is usually pendent, and in some forms is 

 retractile within the fold of integument surrounding the anus. 

 The uterus is bicornuate, and often without a distinct os uteri, 

 the placenta discoidal, and the mammae which are generally 

 numerous are variable in position. They frequently extend 

 along the ventral surface from the axilla to the inguinal region, 

 but occasionally they are axillary (Galeopithecus) or even post- 

 inguinal {Solenodon). Odoriferous glands are present in many 

 species. They may be just behind the axilla, as in the shrews, 

 or near the anus. 



The Insectivora are, with the exception of the Tupaiidae, 

 nocturnal animals. Most of them are cursorial, but a few are 

 burrowers (the moles), and some are aquatic {Potamogale, Myo- 

 gale). Others again are arboreal (Tupaiidae) a,nd Galeopithecus 

 flits about from tree to tree by means of a patagium as do the 

 flying squirrels. They live on insects and worms. 



They are generally regarded as the most primitive of placental 

 mammals, and perhaps their nearest aUies are the polyproto- 

 dont marsupials. In their dentition and in the structure of the 

 skull and brain they recall the Chiroptera, and by their fossil 

 forms they approximate to the Creodonta and Lemuroidea, 



The primitive characters are the small and smooth brain, 

 the frequent occurrence of trituberculate molars, the absence 

 of a scrotum, and the frequent abdominal position of the testes ; 

 moreover the palate is often fenestrated and the angle of the 

 mandible inflected, and sometimes the anus and urinogenital 

 apertures are surrounded by a common fold of integument, 

 so that there is a kind of cloaca. 



They are widely distributed over the earth's surface, but 

 are entirely absent from the Australian region, and in South 

 America are only found in the northern Andes. 



They make their appearance in the Lower Eocene of Europe 

 and North America. Many of the older forms are not referable 



