XIII 



ANATOMICAL STRUCTURE DISTRIBUTION 



585 



The cloacal arrangement is essentially the same as that of 

 the Lacertilia, but Snakes possess no urinary bladder. The 

 copulatory organs are stowed away beneath the skin in recesses 

 of the posterior lateral corners of the shallow cloacal vestibu- 

 lum. Each organ is generally bifurcated at the free end, 

 and furnished with little spike-shaped, but scarcely horny, ex- 

 crescences. On each side of the outer cloacal chamber, in both 

 sexes, lies a roundish gland with an offensive, strongly-scented 

 secretion ; that of various Boas smells disagreeably sweet and 

 musky. The majority of Snakes lay eggs, but most of the 

 Yiperidae and the thoroughly aquatic kinds, besides a few ter- 



IIIIIIIIVIPERINE. =ECROTALINE 



FIG. 153. Map showing the distribution of dangerously poisonous snakes. 



restrial forms, are viviparous. The egg-shells are like parch- 

 ment, with very little or no calcareous deposit, so that they 

 are always soft ; many embryos are, however, provided with a 

 little " egg-tooth " on the tip of the snout. 



Snakes are intelligent creatures ; some become quite affec- 

 tionate in captivity, but most of them are of a morose disposition, 

 and do not care for company. 



The geographical distribution of Snakes has been dealt 

 with in detail in connexion with the various families. Un- 

 fortunately very few fossils are known. One of the oldest is 

 Palaeophis, of the London clay (Lower Eocene). Eemains of 

 Elapine and of innocuous Colubrine snakes have been found in 

 the Lower Miocene of Germany ; Crotaline forms are known from 

 the Miocene of Turkey and North America. All the Plistocene 



