NOTES. 



383 



16 In the heart, the muscular fibres are striated, yet involuntary ; but the 

 sarcolemma is wanting. 



17 Other names are medullary sheath and white substance of Schwann. 



18 We may, however, infer that the animal functions are not absolutely 

 essential to the vegetative, from the facts that plants digest without mus- 

 cles or nerves, and that nutrition takes place in the embryo long before the 

 nerves have been developed. 



19 This is not strictly true, for the Elm and Oak, the Trout and Alligator, 

 do reach a maximum size. 



20 Scorpions and Spiders properly feed upon the juices of their victims 

 after lacerating them with their jaws, but fragments of Insects have been 

 found in their stomachs. 



21 The real tongue forms the floor of the mouth, and is found as a distinct 

 part in a few Insects, as the Crickets. 



22 In the Marsipobranchii, it is circular or oval. 



23 The mouth of the Whale is exceptional, the walls not being dilatable. 

 The act of sucking is characteristic of all young Mammals, hence the need 

 of lips. 



24r The Ant-eater has two callous ridges in the mouth, against which the 

 insects are crushed by the action of the tongue. 



25 The baleen plates do not represent teeth ; for in the embryo of the 

 Whale we find minute calcareous teeth in both jaws, which never cut the 

 gum. The whalebone is a peculiar development of hair in the palate, and 

 under the microscope it is seen to be made up of fibres which are hollow 

 tubes. 



26 'p ne "tusks" of the Elephant are prolonged incisors ; those of the Wal- 

 rus, Wild Boar, and Narwhal are canines. 



27 "I was one day talking with Prof. Owen in the Hunterian Museum; 

 when a gentleman approached, with a request to be informed respecting the 

 nature of a curious fossil which had been dug up by one of his workmen. 

 As he drew the fossil from a small bag, and was about to hand it for exam- 

 ination, Owen quietly remarked, 'That is the third molar of the under- 

 jaw of an extinct species of rhinoceros. 7 " — Lewes's Studies in Animal 

 Life. 



28 This gap or interspace, so characteristic of the inferior Mammals, is 

 called diastema. It is wanting in the extinct Anoplotherium, is hardly per- 

 ceptible in one of the Lemurs, and is not found in Man. 



29 In the Spermaceti-whale, the teeth are fixed to the gum. 



£0 The Iguana among Reptiles, and Fishes with pavement-teeth, approach 

 the Mammals in this respect. 



31 This movement is called peristaltic or vermicular, and characterizes all 

 the successive movements of the alimentary canal. 



32 Fishes and Amphibians have no saliva, but a short gullet. Birds are 

 aided by a sudden upward jerk of the head. 



33 Fishes and Reptiles have no pharynx proper, the nostrils and glottis 

 opening into the mouth. 



34 This movement of the pharynx and oesophagus is wholly involuntary. 

 Liquids are swallowed in exactly the same way as solids. 



