A. 
THE FACIAL MUSCLES 
OF 
MAMMALS GENERALLY. 
I N the history concerning our knowledge of the facial muscles 
of Mammalia, the works of Georg Ruge mark a new era, 
their starting-point being an actually and designedly comparative 
one: the comparative aim being pursued with all consistency: 
and coupled with the greatest care in investigation. Unfortuna¬ 
tely the papers of Ruge only deal with Prosimite and Primates, 
which groups he worked out first; and the Monotremata, which 
he dealt with later on. Of the other orders of Mammalia no 
such investigations of the facial muscles are on record. Even in 
the domesticated mammals, whose anatomy — next to that of 
man — has been dealt with in the most thorough manner, the 
facial muscles have not been treated in this way. The papers of 
Ruge as we have said only deal with a few groups af Mammals; 
and these groups being very distant from the Elephant, we have 
found it necessary to work out, on similar lines, the facial 
muscles of a series of Mammals of various groups in order to 
form a somewhat broader basis, from which we might estimate 
the facts which we found in the Elephant. The more comprehen¬ 
sive material thus at our command — viz. the investigations of 
Ruge and those of ourselves — have naturally led us to results, 
in some points differing from Ruge * 1 2 3 4 ), which differences will he 
evident from what is communicated in the sequel. 
The Mammals, whose facial muscles in a more or less com¬ 
plete manner are examined by us, are the following: Echidna, 
Ornithorhynchus, Halmaturus, Didelphys, Centetes, Erinaeeus, 
r ) For the sake of comparison with the results arrived at through our investi¬ 
gations and exposed in the sequel, we summarize here the principal points of the 
view of the facial muscles set forth by Ruge in his paper: fiber die Gesichts- 
muskulatur der Halbaffen, in: Morphol. Jahrb. 11. Bd.: 
The whole of the facial muscles is differentiated from (wo muscles, both origi 
naling from the neck, viz. 
I) a superficial layer, platysma myoides. 
II) a deep layer, sphincter colli. 
From the platysma Rcge derives the following muscles: 
1) M. auriculo-occipitalis = m. auriculo-occipitalis nob., from which again a deep 
layer is split off: M. auricularis post. — m. postauricularis nob. 
2) M. auriculo-labialis inf. — m. adductor infer, nob. From this is derived the 
m. trago-anlilragicus — m. posteri septimi nob. 
3) M. mentalis = m. mentalis nob. 
4) M. auriculo-labialis sup. — m. postorbicularis nob., from which the following 
muscles are derived: 
a) M. orbicularis oculi = m. orbicularis oculi nob., from which the m. levator 
labii (= m. nasolabialis nob.) originates. 
Talpa, Myogale, Lepus, Myopotamus, Canis, Nasua, Alces, Ceivus 
canadensis, C. Aristotelis, Bos, Camelus, Sus, Tapirus, Equus, Le¬ 
mur, Nycticebus. The types, whose names are italicized, are those 
which we have examined in the most complete manner. 
A general survey of the facial muscles of Mammals may be 
made in grouping them in the following manner. 
1. PLATYSMA-SPHINCTER-GROUP. 
On the ventral and lateral hinder part of the head (the re¬ 
gion below the outer ear and further forward) and on the neigh¬ 
bouring parts of the neck is developed a three-layered complex 
of muscles, consisting of a superficial, transverse layer, which 
we designate the sphincter superficialis, an intermediary, longi¬ 
tudinal layer, the platysma, and a deep, transverse layer, the 
sphincter profundus, These three muscle-plates are generally all 
present, but often the sphincter superficialis is restricted to the 
neck alone, not reaching the head. 
The sphincter superficialis (PI. 17, fig. 1) is in many forms 
a true sphincter, the right and left part of the muscle running 
ventrally into each other. It is most powerfully developed in 
Echidna (PI. 10, fig. 1, 2) and Ornithorhynchus, where it forms a 
continuous muscular plate underneath the neck and the head, 
proceeding unto a line from the outer ear to the angle of the 
mouth. Similarly, in Centetes (fig. B) it is a vei'y strong muscle. 
b) M. depressor helieis = m. scutularis, ventral portion, nob. 
c) M. helieis = ra. anteri sexti nob. 
il) M. orbilo-aurkularis = m. scutularis nob., from which again are derived 
the m. auricularis sup. (= pars transiens nob.). 
From Hie sphincter colli (= m. sphincter profundus nob.) Ruge derives the fol¬ 
lowing muscles: 
1) M. depressor tarsi = portio palpebralis m. sphinct. profundi nob. 
2) M. orbicularis oris = pars ritnana m. bnccinalorii nob. 
From the last are derived: 
a) M. caninus — part of pars rlmana nob., inserting into the maxillary hone, 
b) M. nasalis = m. nasalis nob. 
c) M. maxillolabialis — m. maxillolabialis nob. 
d) M. buccinatorius = m. buccinalorius nob. 
Finally Huge enters the m. mandibulo-auricularis (= m. temporo-auricularis nob.) 
as a muscle independent of the system of facial muscles; his motive of this opinion 
is that ho has not been able to find a branch of the n. facialis to the muscle, 
which he is of opinion is innervated by a branch of n. trigeminus and therefore 
should be regarded as standing in nearer relation to the masticatory muscles. 
