AND PHYSIOLOGY. 



85 



The Radiata he divides into nine classes : 1, Echinodermata ; 2, Bryozoa; 

 3, Anthozoa; 4, Acalephae; 5, Hydrczoa ; 6, Coelelmintha ; 7, Sterelmintha ; 

 8, Rotifera ; 9, Polygastria. 



1 89. To the above Animal Kingdom Pro£ Owen has added another kingdom ol 

 organisms, " mostly of minute size, .and retaining the form of nucleated cells, 

 which manifest the common organic characters, but without the distinctive 

 euperadditions of true plants or animals." These he calls Protozoa, and ar- 

 ranges in three classes : 1, The Amorphozoa, or Sponges; 2, the Rhizopoda, 

 which are the Polythalamia, or Foraminifera ; 3, the Infusoria, or Animalcula 

 y-the last two classes being mostly microscopic. 



COMPARATIVE OSTEOLOGY. 



191. Microscopic Structure. — In microscopic structure and 

 chemical composition the bones of mammals, including man, 

 and of all vertebrates are essentially the same, and in their 

 general outline a considerable degree of correspondence can 

 be traced between many of the bones of the human system, 

 and those performing similar functions in the lower animals. 

 Thus wef almost always find the femur to have a globular 

 head on its upper extremity supported by a neck which makes 

 a considerable angle with the shaft, and the two large con- 

 dyles on the lower extremity. 



192. Spinal Column of Mammals. Cervical, Dorsal, 

 Lumbar, Sacral, Caudal Vertebrae. — In Mammals the Spinal 

 Column is made up of five classes of vertebrae : the cervical, 

 of the neck ; the dorsal, of the back ; the lumbar, of the loins ; 

 the sacral, of the hip ; and the caudal, of the tail. The Cervi- 

 cal vertebrae, with but two or three exceptions in all mammals, 

 consists of seven in number. The average number of the Dor- 

 sal is thirteen, the Bats having eleven, and one of the Sloths 



191. What is the microscopic structure of the bones of Mammals ? What about the 

 general correspondence in outline, etc. ? Instance the femur. 192. What are the fivo 

 classes of Vertebras ? How constant is the typical number seven for the Cervical ver- 

 tebne ? Give the average number of the Dorsal. 



