124 



toericoid of Merkel), mentions, that it is always in females that he has 

 found it ; but Professor Turner has found it in males as well, and 

 I have likewise seen it in both sexes. 



The proportionate frequency of the occurrence of variations in indivi- 

 dual muscles is likewise a point of interest. I have found the muscles 

 most frequently abnormal to be the following, which I have grouped in 

 the order of frequency of variation : — 



1. Palmaris longus ; 2. flexor digitorum longus pedis et flexor 

 hallucis (alterations in their mode of union) ; 3. biceps flexor cubiti ; 

 4. extensor ossis metacarpi pollicis ; 5. pectoralis major; 6. coraco- 

 brachial ; 7. digastric ; 8. peroneus tertius ; 9. zygomatici. From 

 this list I have excluded such muscles as risorius Santorini, sal- 

 pingo-pharyngeus, pyramidalis abdominis, psoas parvus, whose fre- 

 quency of absence is often nearly as great as their presence. During 

 the past session I have preserved records of the presence of some 

 of these rare muscles in the subjects examined, and they are as 

 follows : — 



Azygos pharyngei . . 



. 1 



in 



60 





1 



in 



20 



Levator claviculae . . 



. 1 



in 



60 



Peroneus tertiu3 . . 



3 



in 



4 



Rectus sternalis . . . 



. 1 



in 



30 



Peroneus quartus . . . . 



1 



in 



8 



Zygomaticus minor . . 



. 1 



in 



3 



Peroneus quinti . v . . . 



1 



in 



5 



Palmaris longus . . 



. 3 



in 



4 



Extensor ossis metatarsi 



h 



in 



60 



Subscapulo-humeral . 



. 1 



in 



3 







. 1 



in 



3 











"With regard to the producing causes of anomalies, we cannot de- 

 finitely pronounce any general principles until the mode of the original 

 formation of the several muscles in the embryo has been thoroughly 

 wrought out ; but they seem to be capable of being grouped into 

 two sets. First, those caused by altered conditions of embryonic forms ; 

 and, secondly, those caused by subsequent faults of development. 

 Muscle germs, not normal portions of the human body, but natural to 

 other animals, are often found as anomalies, and can only be explained 

 in one way — namely, the tendency which all animal structures exhibit 

 of wandering towards a primordial or archetypal symmetrical form, to 

 which neighbouring animal individuals are related, either as parallels 

 or descendants. There seems to be a typical muscle system in verte- 

 brate animals, as there is a typical skeleton — a starting point from 

 which all the muscular arrangements of the varied species have been 

 originally modelled, and towards which they continually tend to revert. 

 To this class, also, belong those classes of muscular duality depending 

 upon vegetative repetition; and many instances of suppression are 

 referrible to the same set of causes. On the other hand, the cases 

 of muscle fission, coalescence, and some cases of suppression, are due to 

 the varying conditions of development of contiguous muscles; the 

 first and last depending en deficient growth ; the second upon exuberant 

 development and union from excess of formation : hence, the latter is 

 usually associated with increased muscle power, and the former with 

 weakness ; and all these may be produced in adults by subsequent 



