32 Anatomy otf the Rabbit. 



(b) The secondary bone skull (osteocranium), replacing (a) and 

 comprising the occipital, sphenoid, ethmoid, inferior turbinal, 

 and periotic bones; 



(c) The associated derm elements, comprising the interparietal, 

 parietal, frontal, nasal, vomerine, lacrimal, tympanic,* and 

 squamosal bones. 



2. The VISCERAL CRANIUM (cranium viscerale or splanchno- 

 cranium), including; 



(a) The primary mandibular and hyoid f visceral arches (embry- 

 onic) ; 



(b) The secondary elements, replacing (a) — the malleus, incus, 

 and stapes of the auditory chain; the hyoid bone and its 

 connections with the skull ; 



(c) The associated derm elements of the face and palate, com- 

 prising the premaxillary, maxillary, zygomatic, mandibular, 

 palatine and vestigial pterygoid bones. 



The anterior and posterior portions of the appendicular skeleton 

 include each a proximal or girdle portion and a distal portion, the free 

 extremity. In each the free extremity is divisible into proximal, middle 

 and distal segments. The proximal joint of the limb, either of the 

 shoulder or hip, is an enarthrosis, although it will be seen by examination 

 of the rabbit that the glenoid cavity of the shoulder is not greatly 

 elaborated as a concave surface. The distal joints of the limbs conform to 

 the type of the ginglymus, and with minor exceptions the movements are 

 restricted to one, namely, the sagittal, plane. In each limb they are 

 described as movements of flexion and extension, since the general effect 

 of movement is to bend or straighten particular parts on one another. 

 Similar motions are observable in the limb as a whole, but are not spoken of 

 as of flexion and extension, since the shoulder and hip joints are of a totally 

 different type. In the limb as a whole, the chief motions are of pre- and 

 post-traction, but it is convenient to recognize also movements of ad- 

 duction (toward the body) and of abduction (away from the body). In 

 both cases the axis of the upper arm, or of the thigh, is assumed to be 

 parallel to the median vertical plane. 



In mammals, as in other terrestrial vertebrates, the anterior and 

 posterior limbs are equivalent part for part. They are said to be 

 serially homologous or homoplastic. There is, however, particularly in 

 the mammalia, a pronounced difference between the anterior and 

 posterior limbs in the respective positions of the different segments. 

 Consequently, in studying the related musculature, it is advisable to 

 consider not only the functional relations of muscles, but also the equival- 



*The identification of the tympanic as a derm element has been questioned. 



fThe thyreoid cartilage of the larynx and its connection with the hyoid 

 (greater cornu) are modified branchial arches, but the structure as a whole is not 

 included with the head skeleton. 



