102 PROFESSOR STRUTHERS. 



B. musculus (pis. xii. and xiii.) does not show the great expansion 

 of the ends of the spines presented by this B. musculus. 



27. LENGTH, BREADTH, AND THICKNESS OF THE SPINOUS 

 PROCESSES. In length the processes increase from the 1st dor- 

 sal (3J inches) to the 5th lumbar (the 5th, 6th, and 7th lumbar 

 each 14 inches), and decrease from the 8th lumbar to the 10th 

 caudal (f inch). The longest transverse processes are the six 

 before the above group of longest spinous processes. 



The breadth of the processes at their middle does not vary 

 much from the middle of the dorsal region to the earlier part of 

 the caudal, the broadest being the last lumbar and 1st caudal 

 (5J inches). The expansion at the top follows the same order, 

 about J inch to 1 inch broader than at the middle. The 8th 

 and 9th dorsal come in exceptionally as broad at the top (6 

 inches) and are nearly as broad at the middle (5J inches) as the 

 last lumbar and 1st caudal. 



In thickness the spines increase backwards to the 1st lumbar, 

 and decrease backwards from the 2nd, but the difference is not 

 great. From the 4th to the 7th dorsal it is 1 inch ; on the 

 next three, it is 1 J inch ; on the remaining four dorsal, 1 J inch ; 

 on the 1st and 2nd lumbar, If inch ; on the 3rd to the 8th 

 lumbar, 1 J ; on the 3rd and 4th caudal it is again 1 inch. 



The thicker part of the process is generally behind the middle. 

 This is seen on the top by the generally greater thickness of the 

 posterior third of the border, giving it a narrow ovoid form. 

 This ovoid upper margin is seen from the 8th dorsal to the 

 8th lumbar (10th dorsal, at middle 1 inch, behind 1J; 14th 

 dorsal, 1J and 1J), is most marked on the 1st lumbar (1J and 

 If), and then diminishes backwards. From the 9th lumbar 

 to the 2nd caudal it is absent, and is again seen to a moderate 

 extent on the spines behind that. On the last dorsal and two 

 first lumbar, the thick part of the ovoid end is thicker (by f- inch) 

 than the thickest part of the middle of the shaft ; but, taken at 

 the middle of the ovoid, so as to give an average thickness, the 

 end of the spinous process is generally thinner than the shaft 

 by from to f inch. 



28. DIRECTION OF THE SPINOUS PROCESSES. The spines of 

 the 1st, 2nd, and 3rd dorsal are directed backwards, owing to the 

 greater slope of their anterior border. The 4th, at first some- 



