For a while I thought this was referring to the muscles of the face, particularly as this involved muscle injuries.
However, I could not find "maxillary muscles", only "maxilla", "maxillae", or "maxillary bones", hence my conclusions

Anatomie cranio-faciale - Campus Cerimes
http://campus.cerimes.fr › site › html

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1 Sept 2011 — l'espace rétro-zygomato-maxillaire, occupé par le corps adipeux de la bouche et le processus coronoïde de la mandibule sur lequel se fixe le ...



Chirurgie maxillo-faciale et stomatologie: Réussir son DFASM ...
https://books.google.co.uk › books

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Collège national des enseignants de chir, ‎Pierre GONDRAN • 2021 • ‎Medical
La fosse infratemporale comporte elle-même trois parties : • l'espace rétro-zygomato-maxillaire, occupé par le corps adipeux de la bouche et le processus ...

http://docplayer.fr/31895707-Anatomie-de-la-tete-et-du-cou.h...
see page 10

A
.
Étages
:
1
.
Cr
â
nial
:
Fronto
-
orbito
-
ethmoïdal
2
.
Moyen
:
Naso
-
sinusien ou Maxillo
-
zygomatique
3
.
Caudal
:
Buccal ou Mandibulair


Strhttps://www.ncbi.nlm.nih.gov/books/NBK537034/ucture and Function
The structure of the infratemporal fossa is formed by osseous boundaries located inferiorly and medially to the zygomatic arch. The shape of the infratemporal fossa can be loosely described as an inverted square pyramid containing directional boundaries that delineate its area. Anteriorly, the boundary is formed by the posterolateral surface of the maxillary sinus. The ramus of the mandible forms the lateral boundary while the medial pterygoid and tensor veli palatini muscles form the medial border. The medial border of the infratemporal fossa is continuous with the pterygopalatine fossa. The medial pterygoid muscle attachment to the mandible also forms the inferior border. The lateral pterygoid muscle is located anteromedially to the infratemporal fossa. The posterior boundary of the infratemporal fossa is broadly defined but includes the styloid process and the tympanic part of the temporal bone. Since it an anatomical landmark in the head and neck, the infratemporal fossa functions to house and protect a wide variety of nerves and vasculature that course through the space.[1][3]
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Embryology
The infratemporal fossa encompasses a space that contains a wide variance of embryologic derivation. The mandible and the maxillary artery are formed from the first pharyngeal arch, also known as the mandibular arch. Other anterior bones of the face that participate in the boundaries of the infratemporal fossa, including the maxilla, temporal bone, and zygomatic bone, derive from the mesenchyme of neural crest cells and undergo membranous ossification.[




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Note added at 5 hrs (2021-10-01 22:41:39 GMT)
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I think it is the bones, particularly in light of reference to "paravertébrale et iliaque droite", see:


une observation rare Para vertebral and iliac chondroblastomahttps://anafrimed.net › chondroblasto...· Translate this page
Les auteurs rapportent ici, un cas de chondroblastome de localisation inhabituelle (para vertébrale et iliaque droit) associée à une varicocèle bilatérale ...

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Note added at 5 hrs (2021-10-01 22:50:07 GMT)
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having said all that, this sentence gives a clue too

l'espace rétro-zygomato-maxillaire, occupé par le corps adipeux de la bouche et le processus ...

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The buccal fat pad (also called Bichat’s fat pad, after Xavier Bichat, and the buccal pad of fat), is one of several encapsulated fat masses in the cheek. It is a deep fat pad located on either side of the face between the buccinator muscle and several more superficial muscles (including the masseter, the zygomaticus major, and the zygomaticus minor).[1] The inferior portion of the buccal fat pad is contained within the buccal space. It should not be confused with the malar fat pad, which is directly below the skin of the cheek.[2] It should also not be confused with jowl fat pads. It is implicated in the formation of hollow cheeks and the nasolabial fold, but not in the formation of jowls.[3]

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Note added at 6 hrs (2021-10-01 22:57:06 GMT)
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This is an extremely difficult one!

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Note added at 6 hrs (2021-10-01 22:58:19 GMT)
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l'espace rétro-zygomato-maxillaire, occupé par le corps adipeux de la bouche et le processus coronoïde de la mandibule sur lequel se fixe le ...

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Note added at 6 hrs (2021-10-01 23:07:43 GMT)
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problem is I cannot find an English equivalent

i.e.

the retro-zygomatic-maxillary space is occupied by the buccal fat pad and mandibular coronoid process!